I am indeed speaking of Wine 64bits on FreeBSD amd64 to run 64bits Windows programs
I already know about the awesome wine-fbsd64 builds.
Do I need more than 4 Gb of RAM? I probably don't "need" it but my computer has 16Gb of ram right now and I heard that at least on windows the 64bits World of Warcraft client can up your game performance a little bit. Which could be nice.
And yes, recent version of wine can be made to run 64bits applications. you can even set it up to run both 32 and 64bits actually by building both versions from the same source http://wiki.winehq.org/Wine64