CPU debate

[rooter]

I had initially thought that I wanted to put the fastest single core 32bit CPU into my MAME cabinet to get the best bang for the buck.  I have read and talked with a few people that lead me to believe this might not be the best idea.

The first and biggest thing that I noticed was that there is a  64bit version of MAME for Linux.  Supposedly, using the 64bit compilation is 17% faster than the 32bit.  Can anyone verify this?  Does anyone know if, in general, Linux boxes run MAME faster or slower than a windows box?  Has anyone ever run a 64bit version of MAME in Windows?

I have also heard that in a dual core set up, if you put all your PC's processes on the 1st CPU and run MAME on the second, you can see a noticeable improvement on some games.   

I prefer Windows, but I am familiar with Fedora so I would switch in a heart beat for the 17% performance increase.  If there is a 64bit windows version of MAME in the works, I could wait it out.  I was told the best option would be to use a version of Linux without a GUI, but I would rather not do for various reasons.

So which one?
The Intel Pentium 4 651 3.4GHz 2MB      for $77 seems like a good bang for the buck.
The Intel Pentium D 915 2.8GHz 2X2MB  for $76 Dual core and 64bit seems like it could eventually be superior, but I don't think it would be at the moment.