Should be like night and day. I just upgraded from an 8800GT 512MB to the GTX 260 in my sig, and that was even like night and day to me. It gave me right at 3,000 more 3DMark 06 points (from 15,600 to 18,600). FPS wise the GTX 260 should give you at least 20 more FPS (with vsync, more with the frames uncapped), at least. How much ram was on the 7800GT?