Dear serverfault knowledgeables, im in a decision dilemma right now, which I can't resolve due to lack of hands on experience.

I need to build a testbed for basically virtualizing a LAMP application (os'ses not yet decided) including server side calculations. I'll opt for XEN since it seems better supported by cloud hosters at the moment. The hardware is for a proof of concept for a startup doing saas and might be used for closed live alpha/beta later on.

After testing, the testbed might be

a) deployed as a colocated white box server

b) used as workstation

• Single socket is enough.
• We want to have ECC memory for reliability, this excludes most of the consumer line at intel.
• If intel CPU, then threaded cpu (HT) is preferred
• have at least 16 gig ram
• If justified by price and reliability is not too bad, a high quality desktop MB instead of a server MB would be worth a try

It came down to the opteron 6128 vs. the xeon 5620 for me after a lot of research, but I don't necessarily have to be right.

Which CPU is preferrable, concerning TCO (MB price, power requirements 24/7...) , Opteron 6128 or Xeon 5620? Which one offers better performance in real world applications? (Do You have any other suggestions I probably overlooked?)

Thank You for Your consideration