Since you already have an XP 3200+ build and neither of your remaining Socket A boards have the 4-pin aux 12V connector, thus necessitating the use of a PSU with a very beefy 5V rail, I would go with the P4 for the second system.

I built a Socket 462 Athlon XP 3200 system with an ASUS A7V600 motherboard and then a Socket 478 3.4Ghz Prescott system with an Intel D865GLC motherboard. Just nice to have both systems for diversity. I would go with the P4 system too.

I have both, too. AXP 3200+ with nForce2 and Radeon 9800 Pro in one build, P4 3.06 HT with Intel chipset and FX 5950 in the other one.
Because I was in the AMD camp back in the day, I am more nostalgically attached to the AMD build. But both are solid performers, so it really comes down to personal preference I think.
But as you already have one similar socket A build, I'd say go the Intel route this time...

A P4-HT will outperform an Athlon XP in most cases (although there is some overlap).

I would go with Northwood P4-HT, not Prescott. There are no real advantages to the Prescott core in a single-core, HT-enabled, ~3GHz CPU, and the 800MHz FSB Northwoods are from 2003, so they are even more "period-correct" in your case. However, since you already have a Prescott CPU, I guess I'd just use that.

Actually there could be quite high advantage when overclocking is considered. Late Prescott steppings can easily achieve 4 Ghz with little to none voltage increase. While Athlon XP is quite efficient, when it comes to IPS, it simply can't compensate 60-80% clock difference (Athlon XP upper limit is 2300-2400 Mhz).

Also Pentium 4 is better for DOS setup.

The P4 at 3+ GHz and 800MHz FSB is overall faster than Athlon XP, but both are overkill for any game that runs in Windows 98. Plus the i865 chipset is overall rock solid. But I would definitely prefer Northwood over a Prescott.

But many Athlon XP have an unlocked multiplier, which makes them more interesting for speed sensitive games.

But since you alredy plan to build anothet Athlon XP rig, might as well go with a P4 in this case.

But many Athlon XP have an unlocked multiplier, which makes them more interesting for speed sensitive games.

Technically no, because you can directly throttle Pentium 4, while Athlon system can be throttled only via ACPI. And you have to throttle anyway, because absolute minimum that normal Athlon will allow is 500 Mhz.

I guess it depends on what you want to achieve. I have both the A7V600-X and the P4i65G, so I can give you my two cents.
I paired the P4i65G with a Pentium 4 Northwood 3 GHz and a GeForce FX 5900. It's a fine, stable system, very fast in Windows 98 and acceptable for early Windows XP games. But other than that, there's nothing special about it.

On the other hand, I paired the A7V600-X with an Athlon XP 1700+ Thoroughbred (easily overclocked to 2 GHz, so Athlon XP 2400+ level), a GeForce 4 Ti 4200, a Voodoo 2 and a Yamaha YMF724F-V card.
What is awesome about this board is the fact that you can downclock the CPU to 500 MHz (if the CPU has an unlocked multiplier), and it also gives you the option to disable either the L1 or the L2 cache (or both). So you can slow it down to 386, 486, Pentium MMX speeds. And since the VIA chipset is also great for ACPI throttling, you get even more granular speed control. The board is also rock solid, comparable to the P4i65G, haven't had a single issue with it. Consequently, this is one of my favorite PCs that I own, a real time machine, capable of running 98% of the DOS games I tried, all Windows 95/98 games and even some very early Windows XP games. I also have two other Athlon 64 time machines, and they're also very good, however they lack the granular level of control that the A7V600-X has.

If you go with fast MHz P4 make sure you have good airflow. I tried putting 3.4GHz P4 Northwood with ATI9800 Pro in an old midi size case and the CPU got extremely hot inside the case even when idle. The case had one small front fan and one exhaust fan, plus power supply exhaust fan, but it was a cramped midi size so the airflow just wasn't there. I think the CPU was showing 70 degrees Celsius and the rear fan was blowing out hot air. When I removed side case panel, the CPU went down to normal temperatures. When using 2.8GHz P4 Northwood temperatures were ok.

Cheers for the suggestions, I guess I'll go with the P4 as the 2nd system.

I'll keep the comments re- the Asus A7V600 in mind though, I have 3 Socket A CPUs that I could use in that board to experiment with the underclocking & throttling abilities at some point.

If you need an electric heater go with the P4. If you need a computer go with the AthlonXP.

Too bad that you can not "like" a comment here. But yes I second that. Athlon is way better retro machine than a P4. I was a strange time in our computer history. Golden times of P3 were over and the renesiance of Core2 was around the corner.
Athlon (XP) was the best bang for the bucks. Athlon 64 was also little bit ineffective in my opinion.

appiah4 wrote on 2020-10-12, 12:54:

If you need an electric heater go with the P4. If you need a computer go with the AthlonXP.

Well, he already has an AthlonXP, so might as well use a P4 as the second build.

I'm not entirely certain on the exact 'electric heater' status. Back in the day, it was known that Prescotts run way hotter than Northwoods. I still have nightmare from my attempted Prescott build with a generic case and a stock Intel HSF. That thing idled at 60C according to BIOS sensors, the cooler ran at maximum speed and was so noisy you couldn't use the computer, and the CPU went up to ~80C at which point the thermal protection would reset the PC. I replaced it with a Northwood, which, according to the BIOS sensors idled at about 40C (about 20C cooler), and even the stock HSF was not too noisy (eventually I did replace that with an Arctic Cooler Super Silent 4).

However, in later years, I read something that claimed that Prescotts did not actually run so much hotter (or at all), but that it was just a matter of using different sensors / different locations to detect the CPU temperature, so simple temperature comparisons of Prescott to Northwood were not apples-to-apples. I don't know what the final verdict on the subject is/

Cyberdyne wrote on 2020-10-12, 13:04:

Too bad that you can not "like" a comment here.

Actually, I'm glad there isn't. Forums where such a feature exists tend to deteriorate into popularity contests and like whoring.

dr_st wrote on 2020-10-12, 13:40:

However, in later years, I read something that claimed that Prescotts did not actually run so much hotter (or at all), but that it was just a matter of using different sensors / different locations to detect the CPU temperature, so simple temperature comparisons of Prescott to Northwood were not apples-to-apples. I don't know what the final verdict on the subject is/

This is definitely not accurate. I tested both Northwood and Prescott CPUs, and you can easily tell the difference without reading any sensor information - just touch the heatsink with your own fingers 😁

I've also have a few "duplicate" PC builds (couple of 486's, pair of Slot 1 and a Slot A builds.
You'll have your favorite that you always goto first.

The "trick" is to differentiate the other enough to force you to use it.
AMD vs Intel is always a good start. but I'd also recommend competing brand of soundcard, graphics card, Maybe even OS.

If I had to build a Athlon XP config with the 3200+ I'd go for the rare KT880 chipset mainboards having dual channel ram support and SATA. But still the Pentium 4 @ 3,4Ghz Prescott has something to say considering having SSE3 support too with the right chipset and DDR2 even possible Socket 478 rare mainboards.
For a time correct o.s. and games it'd probably not make much difference but if newer o.s. and apps are intended to be installed the P4 is probably more interesting even if it gives some difficult time on the power usage and the mainboard regulators. I had to put heatsinks on a mainboard voltage regulators (still hot as hell) to just use the latest Northwood, let imagine the Prescott.
I dont remember if the KT880 mainboards for the XP had the 12V four pin connector and did offload the 5V requirements of a Barton based config but still a strong PSU will ever be needed.

and SATA

SATA is semi-useless on KT880 due to hardware bug with SATAII drives.

The Serpent Rider wrote on 2020-10-12, 16:32:

and SATA

SATA is semi-useless on KT880 due to hardware bug with SATAII drives.

I concur. I also have an Asus A7V880 and even though it's a fine board (and it does have SATA), it's still better to go with PATA drives (or SATA to PATA adapters).
Worst of all, at least the board I have, lacks the L1 / L2 cache BIOS toggles that are found on earlier Asus KT600/KT400 boards, so you lose a lot of flexibility when it comes to speed fine tuning (even though setmul can still be used for L1 cache toggling, it's not enough).

Interesting I didn't know that, thanks!