Some of my results that I would like to share with the community:
2x Xeon 2667 V2: 1200-1300 H/s. Power consumption of each CPU: 100W
2x Xeon 2690 V1: 950 H/s Power consumption of each CPU: 100W
So yes, you can make good returns with CPUs you already own. I just happened to have these workstations: not sure I would have recommended anyone to buy these just for mining!
Oh: added benefit. No need for heating at home

I have 2x Xeon E5645, not making much from mining, but indeed heating is not an issue in that room