Could always go with a 3850 512MB and not need a new PSU. Would still offer top of the line gaming but for like half the price. Id expect a 8800GT to be seriously bottlenecked on your CPU too. A 3850 less so.
Could get a nice custom cooled version too.
CM Stacker 830 | Asus P45 P5Q-E | Q6600 - 9x378 - 3400 | 2x 2GB CORSAIR XMS2 DHX 760mhz | 2 x Palit 4830 625/1880 CrossfireX | WD740 Raptor - OS | WD3200AAKS - Games | 2nd WD3200AAKS - Storage| Custom WC'ing for CPU