X850Pro is actually worse than the 6800GT. Remember what I said about GeForce 7 and 6 and anything below a Radeon X850XTPE? Only the X1000 series of Radeon cards have Shader Model 3.0 support. Since all the other Radeons lack it (and anything above and including GeForce 6 supports it) that gives the GeForces about a 500 point increase or so, I'd guess.
Shader Model 3.0 (name for Pixel Shader 3.0 and Vertex Shader 3.0) is something used in all modern (respectable) games. You don't NEED it to run the game, but its a performance booster and cards that have it will perform better and also will support more "eye-candy."