Mainframes (big computers) were always 64 bits(IBM) or 48 bits(Burroughs) even in those days with a memory of only 100KB. The only advantage of 64bits is how much memory you can access (physical or virtual), there are no advantages in speed. Today 32 bits processors access memory by a 64 bits bus and you don't need in most cases 64 bit registers. In special cases that you may need it you have the 64bits MMX registers. The problem is that software designed to realy run 64 bits processors with a 64 bit memory access will not run on 32 bits machines, so you will need two versions of the software. If some software says that can run on both it means it is running 32 bits with the limit of 4BG or Microsoft's 2GB.

Stupidity also evolves!