I know. They way I've got it set up right now (and plan to do with my 8600s), I don't have it in SLI for general working/surfing/etc, plus playing FSX. When I'm in a game other than FSX, I switch it into SLI.
You obviously haven't tried FSX.
You know how HL2 is known for being very CPU dependant? Take that and multiply by 10. I see very little difference in going from a single 6800GT to an 8800GTS. There is literally ZERO difference in going from 640x480 to 1600x1200 or going from Very Low res textures to Extremely High res textures, but move the auto-gen scenery from None to Sparce and your frame rate drops 20 fps.