I purchased 2 GF7800GTXs and SLi'ed them on an ASUS A8N motherboard with AMD64 3700 CPU. It absolutely rocks, especially as I have a Dell 24" 2405 TFT and play all games at 1920x1200 with full AA. This replaces my 3.2GHz P4 with single 6800GT card, which struggles at 1920x1200 without AA.
I play FAR Cry with HDR enabled and get about 20 FPS (which is playable), not bad considering 2 6800 gives you about 10 FPS. With no HDR, I can run Far Cry at 1920x1200 with everything full on, and it does'nt even flinch.HDR does impact even the GF7800s.
This system is a bit of an overkill for CMBO, CMBB, CMAK but I have noticed that the AMD64 Athlon is a better processor than the Pentium 4. Some huge battles in CMBB now take on average 1 min to process the AI, as opposed to 2 mins on the P4.