Interesting read I came across the other day:
http://www.techspot.com/review/1155-affordable-dual-xeon-pc/
Long story short, there are a lot of Xeon E5-2670 on the market (used) and it is possible to get a pretty respectfully high performing system for a bargain price.
Not the highest of clock speeds, but a 20Mb cach is not to be sniffed at, and 8 cores..
Thought I'd share