Apparently there are some confusions about what a 64 bit system is. You don't need to fear that your processor uses "only 32 bit of its address and data buses" under Win32. The difference is software only.

In 32 bit mode, the processor uses 36 bits for addressing RAM, meaning a 64 GB limit, but Win32 supports less than 4 GB. In 64 bit mode, the processor on a normal PC does not use any more address bits, but the OS can now use the full address range. Thus when you have 3 GB RAM or more, 64 bit programs will indeed run a little faster due to more effective memory management.

A separate 64 bit version of Gamestudio will become eventually available, but not so soon. The advantage is not big and 64 bit OS are still the minority.