What kind of power use were you seeing on 2660/2680s?I found those to be really picky about mining configuration to get decent performance. Best I could get on Dual E5-2650v2 was 3350 H/s with all cores enaeld, which I was pretty happy with.
Personally I like the E5-2680v2 as it has the highest hash per watt and is a reasonable price.
Total system cost, the $/hash not quite as good on the E5-2680v2, but when you factor in power costs, the value of your time, residual value down the road, and the per-server cost of miscellaneous hardware, the E5-2680v2 is more appealing.
Trying to figure out how big I can go without requiring an upgrade to my electrical panel.