Which one has better performance? The 64-bit version or 32-bit version of Windows 7? I have a Core i7 950 and 12GB of RAM, so no problems there (installed using UniBeast).
Get the 64bit version unless you have some very exotic DOS application(s) that requires 16bit support (not available on the 64 bit version). There isn't that much notable difference in terms of performance, but 64 bit is the future, and since you have a good amount of memory you can assign more than 4 GB to the VM, a 64 bit OS can make full use of more than 4GB of RAM and allow apps to use more than 4 GB. Also in the future it is likely that many pro apps will start coming only in 64 bit flavor.
