A few general observations, you can make your specific picks, brand loyalty never allows a person to be objective.
Windows XP is old, insecure and only supports DX9. Use Windows 7 x64 for your next build. It will work just fine for gaming and does not have any impact on frames, anyone who tells you otherwise, does not know what they are talking about. Period.
On the video card front, it is trending towards an all ATI world, at least in the not too distant future. Nvidia is desperate to branch out and be more than just a PC graphic card vendor. Fermi maybe a great card and it may compete with ATI's newest offerings, but I am worried that little Nvidia is spreading itself too thin by trying to be too much.
Regardless of whether you choose to go Lynnfield/P55 or Bloomfield/X58, you will definitely want to go with an SSD for your boot/application drive. That alone will give you the single biggest real world performance boost.