We have tested UR v4 on all x64 (64-bit) Windows operating systems (XP, 2003, Vista, 2008, and 7).
I wouldn't expect much difference in performance vs. running in 32-bit Windows on the same hardware.
I would only recommend installing 64-bit Windows if your machine has more than 2GB of RAM.
http://msdn.microsoft.com/en-us/libr...78(VS.85).aspx