Yes there is a differance. With the 9800 Pro you have the ability to 'flash' it to a 9800XT, resulting in more FPS. This is basically just overclocking it, getting more than what you payed for.
If you honestly are only going to use the card for just those games you'll be more than pleased with anything above a 9800 Pro. The processor also plays a large roll in the FPS and smoothness, the CPU you picked out is more than enough for any of those games.
Benchmark wise the x800 with a similar system to your setup would get around 12,000-13,000 points in 3DMark03. On my stock 9800 Pro I got 10746. That's about 2000 below the x800, I also saved about $150 and will never notice a differance in gaming unless the games get really graphics heavy. I plan on buying a new card in 2 years or so anyways just to keep up with everything.