Hi, I'm currently running WF4 on XP64bits worstation, but I cannot tell you wether or not it's faster. I assume NC toolpath crezation are not implemented in 64 bits algorithm, first I assume (I know it does many assumptions)because you need to build special algorithms for 64bits. And also because we're currently meeting many problems dealings with hudge assembly and the 64 bits configurations do not seems to brings enhancement. What's important it's for your toolpath parameters, tool... to be clean, by this I mean no circular referency or others time consummings problems. For further infos take a look to the follwings links :
http://www.mcadcentral.com/proe/forum/forum_topics.asp?FID=11 and for your hardware configuration follow PTC certified list.