WTF!!! My 9800Xt can play the game max 1024x768 w/ no AA, my 6800GT owns the game like its nothing so your 7800 should have NOOOOO problem whatsoever.
@ the 6800GS, try RMAing it and maybe you will get a good one. I also heard that the AGP version is supposed to OC higher than the PCI-E version casue its just down clocked. On the temps my 6800GT runs full load at 60 and idle 53. I dont think you have to worry about it.
I can play on high 1280*1024 with full AA and AF but once my GPUwarms up and reaches the 60C mark in everest the game starts to lag and sometimes even freezes up my whole PC
