You should read some of Phoronix' processor benchmarks
, specifically on the Intel Core i7 3770K
and AMD FX-8150 Bulldozer
. You should look what benchmarks are relevant to you, the performance using Linux can differ a lot from the Windows performance.
These two processors (with the i5-3570k) are probably the shortlist. Their idle power draw is very similar
, but Intel processors draw less power when loaded and are easier to cool.
I'm not sure if you can cool any of these completely passive, even a very slow spinning fan (<500rpm) will improve the cooling dramatically and is inaudible. I would highly recommend it, especially if you load the CPU with compile jobs for long periods at a time.