I just upgraded from a 6800 to my 8800gt and am seeing virtually no improvement. 3DMark06 gives me about 5300. I get about 17 FPS in Shat in WoW.
My rig is:
Pentium 4 530 (Prescott) 3.0 OC'd to 3.6
Asus P5AD2-E Premium motherboard
2 Gig of Geil DDR2 Dual Channel (PC2-4300 DRAM freq 240.1...