Benchmarking OS- W7 Pro or Ultimate & where to find XP?

Hey guys, I've got a project going here and need some input. I'm going to be setting up a couple of spare SSD's as designated benchmarking drives with Windows 7 and Windows XP- the idea is to be able to just pop them into my systems and benchmark without having to reconfigure the entire OS with the proper applications and services disabled for a clean platform. I intentionally build everything using identical hardware anyplace that would require drivers (wifi/keyboard/mouse/ect), so I think this should work.

What I need to know first is whether or not there is a reason to use Windows 7 Pro or Ultimate over the other- basically is one lighter weight or known to produce better bench numbers? I have both OS discs available to use. The second question is if there is anyplace to still buy or download Windows XP from a valid source? I only have it at the moment as it exists from HP, which includes all sorts of proprietary bloatware I would rather not have to deal with for this purpose.

Thanks

The question would likely be better asked in the benchmarking team section

You can look up some guides on how to strip down an OS for benchmarking.There are also pre stripped ones also available if you search around. (Tiny and micro are commonly used prefixes... that's all I can say).

I don't believe there is a benefit to ultimate vs pro. Just the real goal is to only have the things running that are required (startup and services)