I noticed 64 bit is fairly new and that it's still sort of an unstable OS.
Untrue!

I can't comment on XP64, but Vista64 has proven to be absolutely stable for me, and the upgrade (well, ok, re-installation!) was completely pain free.

So long as you can find drivers for all your hardware (and you will if your machines less than a couple of years old, with mainstream supplier components), it's a walk in the park.