This is a deadly review site and forum:
http://www.thejemreport.com/index.php
I am constantly amazed at how thorough this site is with their reviews and comparisons, just amazded:
http://www.xbitlabs.com/
This is a support forum, but has many categories i ncluding MAC and Linux:
http://www.techsupportforum.com/
I love this site,
http://ncix.com/, I use it to buy parts because it has so many user reviews and discussions (not to mention good price).
Even if I don't buy here, the user reviews are just what I look for, many discussions involve comparisons and troubles that are experienced.
Look for price range first, then read reviews on the products!
PS. There is 'support' for 64 bit with windows, it is a matter of the software. AMD chips are better than Intel last I looked because the Opteron (and probably the FX) architecture supports both 32 bit and 64 bit with the same processor.
Seeing 32 bit software is not going anywhere for quit a while, this is probably the most important consideration.
For servers or something like that, maybe a strict 64 bit may do, but for desktops, you MUST have both.
I also like these reviews at pcmag for being objective and relevent, and they (as well as x-bit) use sisoft, and a host of task specific softwares to compare performance, ie publishing/office tasksvs graphics/gaming:
http://www.pcmag.com/category2/0,1738,22,00.asp
You might find sites like this handy because there are many ways to analyse, like overall system, price etc, and they bring up salient points that a person may not be aware of.
Good luck!