Hi guys,
I'm using 2 x GTX580 in SLI and it does improve the sim for me. However, not in the way that I was expecting.
As most people seem to do, I spent a lot of time testing different configurations and in the end I have settled for almost exactly Word Not Allowed's setup (I think the only difference for me was FFTF @ 0.15. I got too many blurries at 0.1). What the SLI did for me is get rid of artifacts (black flashes, triangles,spikes etc.). When I have just one GPU running, especially around airports like ORBX YBBN I occasionally get vertical spikes, flashes etc. I left MSI Afterburner running in the background and found that I was maxing the GPU out, which surprised me a little! When I tested exactly the same scenario with SLI, both GPUs would run up to about 60% and I'd get no artifacts at all.
For me, SLI seems to make virtually no difference in FPS or smoothness (either positive or negative)
So, that's my experience. Obviously different people might have a different experience.
Ed.