I don't think it'll make that much of a difference, but I can't say for sure, because there are several games that are supposed to support it.
I like my current 6800GT @ Ultra speeds, its run everything that I've played on it at 1600x1200 with 4xAA and however much AF smoothly enough for me. I know the X850 will do that smoother, but thats not an issue.
I'm more wanting to see what differences I see as far as just normal useage and image quality are (for instance 2D desktop quality, movie playback, etc.). I also want to check out the VIVO capabilities of it.