Flagship cards can have good FPS/watt under load, but they all use more power at idle and at low GPU loads. Older games won't load the card at 100% so the FPS/watt will take a big hit. Cards with more memory and wider memory bus consume more power at idle.

Compare these:
GTX 970 4GB = 14.6W at idle
GTX 960 4GB = 11W
GTX 660 2GB = 11W
GTX 650 Ti 1GB = 8W

I don't know about Radeon cards of this generation, but the 4/5/6000 series can be hit or miss. For instance I have a 5570 1GB which throttles to 157MHz at idle and is around 10W maybe? But I have a 5670 1GB which only would throttle to 400MHz and clearly ran hotter at idle (though I never wrote down a measurement).

Some Radeon 3DMark efficiency benchmarks with vsync on at 60 Hz, max resolution and 32 bit. The HD 5770 couldn't go lower than 75 Hz at 2000's max of 1280 x 1024, so it's excluded. All cards averaged 60 FPS except in 2006 and the R7 360 E in 2000 AA. In 2000 the high detail benchmark was used, instead of low as last time. In 2006 the first SM3 benchmark was used.

Peak system Wattage, 1 second window:

Ratio of FPS to average system Wattage:

The R7 360 E was about 30-40% more efficient than the HD 7970 GHz and about 5-15% more efficient than the HD 5770. This time the 5770 wasn't undervolted.

In 2000 with AA, the R7 360 E averaged 57 FPS, so it didn't quite hit the cap. The HD 5770 could do 74.6, so overall for DX6-9 it tends to have similar efficiency plus better performance in the DX6-7 range. In DX9 the R7 starts being faster, but its driver breaks compatibility with 3DMark 99.

Quadro FX 1500. Good efficiency. Looks like good support for DX6 onwards with 90 series drivers, but 3DMark 06 is too demanding so at best no late DX9. Not enough performance for SSAA, besides the drivers don't seem to support pure SSAA.

FPS per Watt, vsynced to 75 Hz in 2000 and 60 Hz in 2003:

Based on more testing, my new top list for best efficiency in DX6-9:

1Radeon HD 7750
2Radeon HD 5770
3Radeon R7 360 E
4Radeon HD 2600 PRO
5Nvidia NVS 300

The first two have similar efficiency up to early DX9, after that the 2600 PRO starts falling off. Both have decent compatibility for early DX and with a 45 W CPU average under 80 W total system draw with a vsynced gaming load as per 3DMark.

The R7 360 E is still the best of the tested for late DX9 efficiency while having decent compatibility with early DX.

An undervolted HD 5770 is the best pick overall for efficiency, compatibility and performance, not perfect in any but best so far if all are considered.

If low performance in mid/late DX9 isn't a problem, the NVS 300 has the best efficiency of the lot. Reasonable compatibility with earlier DX when using driver 260.99 (edit the INF file to make it install).

vvbee wrote on 2025-07-15, 21:33:

Quadro FX 1500. Good efficiency. Looks like good support for DX6 onwards with 90 series drivers, but 3DMark 06 is too demanding so at best no late DX9. Not enough performance for SSAA, besides the drivers don't seem to support pure SSAA.

FPS per Watt, vsynced to 75 Hz in 2000 and 60 Hz in 2003:

The attachment 77c5417611aa.png is no longer available

What are the games you're also using to verify they are rendering without glitches? 3DMark 2000 is DirectX 7, while 99 is DirectX 6. They were used to show off newer features of DirectX releases but aren't a torture test proving a GPU will handle the edge cases. Maybe I'm not seeing it, but I don't see any mention of games you're using to verify DirectX 6-8 functionality.

Did you already torture test the cards and now you're just comparing power draw? You put the constraint of needing support for DirectX 6-9, finding the lowest power draw doesn't mean much if it's backwards compatibility is limited to just the benchmark being used. Drivers were optimized so people saw much higher numbers and increasing lines on the charts versus their old cards. But that didn't translate to the old games working without issue.

Various games, see me on YouTube.

Best FPS/Watt GPU for XP is a 28nm GPU with high ASIC quality and software voltage control.

Nvidia NVS 300. Good efficiency, 18 W TDP is the best Nvidia has to offer in the discrete space. 65 W system draw on an Athlon II and 35 W on a Haswell Xeon. Good compatibility with DX6+, performance good up to early DX9 but without AA.

Quadro K620 can be software undervolted for significantly better performance.

Already tested a GTX 745 from that generation, poor support for DX6-7.

The NVS 300 turned out to have worse support for older DX under XP than in 7, not as bad as newer Nvidia but worse than the FX 1500. The Radeons remain the best when all is considered.

vvbee wrote on 2025-07-31, 20:06:

The Radeons remain the best when all is considered.

Something like a HD 7750 was also my conclusion eventually. Especially by the grace of the iCafe 2015 drivers and its practical OpenGL 3.3 compatibility, combined with good legacy compatibility. Other driver versions may have their own advantages and mainly disadvantages. Must admit though, that I never investigated the later NVidia cards much, after the Geforce 6xxx / 7xxx bumpgate issue threw me off. But I do use a GT 710 GDDR5 under XP once in a while, with driver 344.75, which can actually render Mechwarrior 3, where the Radeon cannot. OpenGL 3.3 is also good on that one.
My take is in here: AMD Catalyst drivers for Windows XP - newer is NOT better - Note that I do not agree with the topic title.
Using a Sapphire Radeon HD 7750 1GB.

Edit: just tried it again and Mechwarrior 3 actually renders with iCafe 2015 driver and DXWnd wrapper.

That really depends. Does that 7750 in particular has voltage control? If not, there are better candidates. Also I consider low profile versions of Cape Verde to be more interesting, because they are tweaked for better efficiency from the box.

The Serpent Rider wrote on 2025-07-31, 21:26:

That really depends. Does that 7750 in particular has voltage control? If not, there are better candidates. Also I consider low profile versions of Cape Verde to be more interesting, because they are tweaked for better efficiency from the box.

I did not dive that deep regarding the Wattage. In my considerations I "assumed" all GCN 1.0, 28 nm as equally efficient per Core/TMU/ROP. Also assumed lower nm process size is key for efficiency. That left only a small selection of obtainable used Radeons in my area / within my TDP preference. Also like the fact that with this Sapphire passive model I am not at the mercy of old cooling fan noises. I added a low speed fan to it myself.
Do have my more tangible observations regarding compatibility with OS and software, with certain drivers.

So far no better candidates than the 7750 have been shown. In my testing the 5770 with its earlier drivers was somewhat more compatible but lower frames per Watt. Undervolting will by default have its influence in the 10% range, may be less than 5% of total system draw, useful but not a game changer.

I would like to see GTX 680 with 306.23* driver tested for compatibility...
*last one supporting everything everything (from GF6 up to Kepler 600 series)

agent_x007 wrote on 2025-07-09, 18:38:

Also, you probably won't be run all DX6 games using DX11 hardware due to late driver issues/incompatibility.
More realistic is DX7/DX8 up to DX9c.

this is a big thing to bring up, more so a problem DX 5 but some dx6 games can be wonky too, but only in hardware 3d mode. software works fine.
you would want to stick to the 5xx line as your newest if you want full dx6 support.but then you have to use very early drivers and you have other bugs to deal with so you are better with the 2xx or 4xx line, 7xxx or older of you want full dx5 support. that or software mode.
That aside wrappers will fix a lot of the bugs and problems with DX11 cards.

that being said OP don't forget load, a sub 50w gpu might sound good but if you are pinging it at 100% load when gaming its not that good and a 100w GPU at say 10% load may end up being better.This is why my gtx 580 pulls far more power then my titian x when gaming, they may both be around the same power draw at max but because the 580 sticks closer to 100% load it pulls more power and dumps more heat.

agent_x007 wrote on 2025-08-01, 16:24:

I would like to see GTX 680 with 306.23* driver tested for compatibility...
*last one supporting everything everything (from GF6 up to Kepler 600 series)

Some years ago I was looking into nvidia driver compatibility for older games and found this topic: My research into when Nvidia broke backwards compatibility with DirectX6 and earlier games

The nvidia forum link doesn't work anymore and I'm unable to load the page with wayback machine, but I do remember the test results clearly indicated 260.99 driver was the last that had good compatibility with dx6, possibly with dx5 too. Everything later caused crashes and glitches.

That would suggest you are limited to GTX 400 series with nvidia if you need Win9x era games to function more or less well without wrappers or other help.

Sombrero wrote on 2025-08-01, 17:00:

Some years ago I was looking into nvidia driver compatibility for older games and found this topic: My research into when Nvidia […]
Show full quote

agent_x007 wrote on 2025-08-01, 16:24:

I would like to see GTX 680 with 306.23* driver tested for compatibility...
*last one supporting everything everything (from GF6 up to Kepler 600 series)

Some years ago I was looking into nvidia driver compatibility for older games and found this topic: My research into when Nvidia broke backwards compatibility with DirectX6 and earlier games

The nvidia forum link doesn't work anymore and I'm unable to load the page with wayback machine, but I do remember the test results clearly indicated 260.99 driver was the last that had good compatibility with dx6, possibly with dx5 too. Everything later caused crashes and glitches.

That would suggest you are limited to GTX 400 series with nvidia if you need Win9x era games to function more or less well without wrappers or other help.

I tried 260.99 and it was not good on hardware 3d dx5 games.

also a working link
https://www.nvidia.com/en-us/geforce/forums/g … highlightresea/

old school gamer man wrote on 2025-08-01, 17:19:

I tried 260.99 and it was not good on hardware 3d dx5 games.

Brute forced the driver in? 260.99 supports 6 - 400 series. You edited the GTX 580 out of your post.

Highly doubt 260.99 has anywhere near perfect backwards compatibility even with supported cards, but those test indicated everything after them were noticeably worse.