Id say the demo version runs a fair bit worse than the full game. The full game has been patched twice, which should help matters plus drivers from both Nvidia and ATI are tuned to the full version, which is a later build than the demo version. Your gt should stomp through the full game, my 2900 pro(STOCK) gets 30fps average in the first half of the game in XP @1400x900 with all on high, with shadows, particles, game effects, volumetric and post processing on medium. Your gt should beat that by a long ways. Try the full thing, fully patched with the new forceware 174, with shadows and post processing on medium. You'll lose like 5% image quality for a substantial gain in fps.