I noticed Sun is providing a 64-bit version of Java. Does it perform better than the 32-bit version?
Almost always 64 bits will be slower.
To quote Sun from the HotSpot FAQ:
The performance difference comparing an application running on a 64-bit platform versus a 32-bit platform on SPARC is on the order of 10-20% degradation when you move to a 64-bit VM. On AMD64 and EM64T platforms this difference ranges from 0-15% depending on the amount of pointer accessing your application performs.
There are more details at the link.