Well, I've got my GTX480-SLI setup working now. I have to say, it's really a bit of a beast. I find it hard to give it enough load to max out both GPUs at 1920*1200. Even with crysis at 1920 with 8xAA I wasn't able to push above 85-95% GPU load!
Anyway... As you probably figured from my previous posts, one of my interests is in microstutter. For some reason people don't seem to think it's an issue, but that's mainly because a) they don't understand what it is, and b) you can't "just see it" from looking at a game.
Anyway, I did a few tests with the program I wrote to examine the GTX480s:
First, the good news: Under less than 100% GPU load there is very little microstutter. For example, crysis at 1920*1200 8xQAA:
Pushing up to 2560*1600 with 4xAA, we see a bit more MS creeping in. Now, I have to say, at full GPU load with my old 4870x2 I was generally seeing a microstutter index of over 20, and sometimes 30+, so in that regard this is an improvement:
As a comparison, I ran the same test with SLI disabled. At first I got less than 50% the framerate which was a bit of a
moment, as 100%+ SLI scaling should be impossible. But it turns out that afterburner resets to default clocks when you disable SLI (even though the GUI still shows the overclock). Anyway, fixing that I get:
... So no microstutter (as expected from a single GPU). The small variation is to be expected from regular game-scene changes.
Now, I know that the microstutter index is a little hard to visualise unless you're used to dealing with statistics, so I plotted the instantaneous framerate variation for the single and dual-GPU setups. I chose a selection of 35 frames to highlight the effect of microstutter. Not all the SLI game scene is this severe, but you get the picture:
Anyway, there you have it. Microstutter is alive and well with the GTX480s. If you can manage to push them to their limits, that is! As always, a single GPU will give you a smoother gameplay experience at a given framerate, but adding a second GPU gives better results than a single GPU overall.
I would really like to see some results from multi-GPU ATI users. I'm not interested for any fanboy gloating type reasons, or even purchase justification - I'd just like to see how the two different technologies handle things. I suspect that they will be very similar.