Luiz,
Sorry for the beginner's question, but could you explain or give some more details on what would be the advantages/disadvantages of a 64-bit PM?
Given a system that has a 64-bit CPU (I think just about all systems nowadays have 64-bit CPUs) a 64-bit application would have a few advantages:
More memory available to the PM application. You could set PM's Memory Cache to several GB if you like (and if your system really has the RAM headroom) and get a lot of potential speedup in caching.
Data can be processed in 64-bit chunks instead of 32-bit chunks. Possibly speeding up image decompression, and transfer of memory from one block of memory to another.
No real disadvantages that I know of for an application like PM.
-Kirk