Correct me if im wrong but isnt it extremely difficult to unlock the XP 2100? I think I would rather buy a 2000 and overclock!
Personally I wouldn't bother unlocking any of the "top end" processors. They are so close to the speed limits anyway, any o'clock, (<200-300MHz), would produce a virtually undetectable boost in system performance. Comparing the XP1600 to the XP2100, the performance difference in real world terms for most people is negligible.