For PC enthusiasts and gamers, moving to 64 bits may not present as many obvious advantages in the near term, but there’s also very little apparent penalty in going with Windows XP Pro x64, even if it’s only to run 32-bit applications. All of our gaming tests showed very little performance delta between WinXP and WinXP x64, and the same was generally true for other apps. Just make sure that 64-bit device drivers are available for your hardware.
64-bit Computing Put to the Test
Source: The Tech Report
Scott over at The Tech Report has taken a good, detailed look at the current state of the 64-bit world by comparing the Athlon 64 and the new Intel EM64T processors against each other in several series of benchmarks.