64-bit computing is far from ready, but it is definitely on the horizon. My experience with x64 has provided absolutely no benefit in performance.
To truly take advantage, you need applications written for it and there is where it falls short today. Very few apps out there today (and I would guess none in this industry) are designed to use the 64-bit architecture.
The bigger issue though really is with hardware driver support. Few manufacturers are providing x64 drivers. Most manufacturers that are working on delivering x64 drivers are doing so for Windows Vista and not XP. So if you plug in a new video card or a new ethernet card, is there an x64 compatible driver available. I would research that first.
I would imagine, although I haven't tried it and it isn't officially supported, that RSLinx and many other apps would probably run just fine. However, I seriously doubt you will see any performance benefit in the x64 environment over x32.
Again, this is for today. Like I said, x64 is on the horizon. At some point everything will probably be 64-bit.