I saw a lot of posts about the expansion of available RAM for 64-bit users, but I didn't see anyone bring up the fact that native 64-bit code gets to use a much bigger and more efficient register set (and additional instructions) within x86-64 CPUs compared to the old i386 register set and it's 32-bit-max small set of registers. Properly used these newer, larger, and more numerous registers can prevent many unnecessary memory accesses outside the CPU complex. I've noticed this bring a lot of headroom to my Sonar use on the same systems (using 64-bit OS + 64-bit Sonar vs. 32). This is why I've always tried getting to 64-bit as soon as possible, but have just done so in the last few years due to a lot of the 32-bit plug in issues a lot of us have been dealing with. I tried XP-64 several years ago and that did show the performance boost, but the incompatibilities were too numerous for me at that time.
But yeah, definitely worth the move now if you are using modern hardware and can deal with some incompatibilities that are reducing as time goes on.