2k pro is for business applications. xp pro is for games. xp home is for pansies. Also, xp is the only current end user MS OS that supports hyperthreading.
If your CPU HAS HT... then get xp pro, regardless what you want to use it for (only in your house, xp pro sucks in the business market - it will bring your sever to its knees.)
If you plan on doing a lot of business type applications AND you don't have HT, then get 2k pro.
Benchmarks show that 2k pro is faster than XP pro (minus HT) for business application.
I guess if you turn off all the crap included with XP, it is most likely faster in for business application.