AnandTech has posted one of their newest reviews of the 64-bit arena. In this review, they take an Athlon64 3500+ (2.2GHz), 1Gb of PC3500, snap in a GeForceFX video card on the newest nForce3 motherboard and give SuSE, RedHat and WindowsXP-64 a whirl.
Surprise, surprise, Linux comes out on top. However, you should check out the individual results of each test to see the quirks and see which of the 2 linux distos comes out on top. Also interesting to note is the hardware intricacies involved in the setup.
append: and if that's not geek enuf for ya, how about a history lesson? ArsTechnica has a nice write-up on the history of the intel Pentium series, and the short-comings and hurdles along the way for the x86-Pentium processor. Good read, you'll learn a little too.