The 64-bit processors won't really offer anything to UF, since the difference between 32-bit and 64-bit deals with integers, not the floating-point math UF uses. (Although theoretically it might improve the deepzooming support, if that were re-written for 64-bit, because deepzooming works by using lots of integers to fake a really big, precise number.)

Things that do matter are CPU speed, floating-point performance, multiple cores (which UF can use), and lots of RAM (if you're using flames). For Photoshop (Mindy's question) lots of RAM and fast disk almost matter more, because at the print sizes she's dealing with, those are the limiting factors.

--Damien