Truth is, there's not much difference performance-wise between 32 and 64 bit. 64 bit was designed to take advantage of high end processors with more than 4GB of memory available. The 32 bit system can only handle 3GB maximum. The main advantage is that 64 bit will remap your system BIOS so that you can make full use of your available memory. Think of it as a performance enhancer similar to boring out the cylinders of an engine.
You may notice a slight improvement in processing speed, but not likely. The big thing is making sure all your current software will support it, or else be prepared to buy new.