6800 Ultra SLI could well be CPU limited with 2004-5 CPUs at 1024x768. It would be interesting to drop them in a more powerful machine and experiment with driver releases...

Something else to ponder is NV4x and R4xx have efficiency fall-offs above 1600x1200.
http://techreport.com/review/8538/uber-high-r … g-on-today-gpus

swaaye wrote:

6800 Ultra SLI could well be CPU limited with 2004-5 CPUs at 1024x768.

That would be my guess as well. I've read that this was the case with early DX10 GPUs, which never approached 100% scaling back in the day but can now do so with the help of faster CPUs. Early SLI is probably less robust, though, so there might be other practical limits.

I experimented with G80/8800GTS (640MB) SLI scaling on my 4.3GHz i7-4930K recently.
I bought these cards back in 2006 and originally used them in a rig with a S939 Opteron 185 overclocked to 3GHz. In that system, SLI generally increased performance by 10-50% under XP and -5 (yeah, negative five) to +10% on Win7.

But on the 4930K machine (Win7), performance pretty much doubled every time. So yeah, I was missing out on quite a bit of untapped performance by teaming up my 2006 GPUs with a 2006 CPU. I'd imagine it would be the same story with 6800 Ultra and S754 A64 or P4.

I only own a single working PCI-E GF 6800 GT/Ultra but I am high bidder on another one. If I win I will try the SLI scaling using a new(ish) system.

SLI/CF scaling, in general, tends to be both CPU and application dependent - there will always be applications that realize little to no benefit, and others that tend to do very well. Having a substantially faster CPU will just amplify the "do very well" category *if* the application is CPU limited. I don't think, however, that it's worthwhile to invest money in a modern TOTL Intel/AMD to hook up 6800s or 8800s or whatever.

With my GF7s there's certainly an improvement in benchmark scores as CPU performance goes up, but even within synth benchmarks they do hit a wall where FPS isn't going up because it's GPU bound and you're at the limit. Same applies if you force them into a GPU-bound situation, like enabling SLI AA. Low resolution, low detail, etc tends to be CPU bounded, so of course a faster CPU will improve it.

Yeah a 2005 platform can certainly benefit from something like a 560 Ti if you are say gaming at 1920x1200. It really comes down to resolution of course. I've been experimenting with X850XT, X1950XTX, 3850 (factory OC 512MB) and 560 Ti lately in a nForce4 + A64X2 setup. There are many situations where even a 3850 becomes a bottleneck. Almost any game from 2005 onward.

I don't have any SLI options to try though. I've always preferred single GPU configs.