I am trying to understand why such a focus on CPU power usage for your application. Usually CPU power consumption is a big deal in a data center where there are dozens or even hundreds of servers running. The cost of power and cooling is significant such a high density environment and companies are willing to pay a premium to get similar computes with less power. In an office or home environment with a small number of servers it can be difficult to justify the cost savings of a low power/high performance CPU. Consider the following options:
Dual Intel L5640 CPUs vs one E5-2630-V2 vs one E3-1230-V6. Each of these CPU solutions provide similar performance on the PassMark tests. The annual power costs (using CA residential power rates, 24/7 usage and 25% avg. CPU usage) are as follows: Dual L5640s: $46.32; 2630 V2: $26.88; 1230 V6 $24.29.
The good news is the 1230V6 (assuming 24/7 usage) will save about $22 a year over the dual L5640s and about $1.50 annually over the 2630 V2. There will potentially also be savings in cooling costs as well. The challenge is the cost of newer CPUs, memory and motherboards, make the older hardware a better value. For example (on eBay) a pair of L5640s will run less than $20. A single 2630 V2 will cost less than $25. A single E3-1270 V6 starts at about $220. Newer CPUs are on a steep price curve compared to older CPUs.
One last thought; If you are looking for lower power and good performance, consider CPUs with an "L" at the end. The 2630L V2 (6 cores) or better yet the 2648L V2 (10 cores) offers quite a bit of performance at less the 75w per CPU. Pair that with a SuperMicro board like an X9SRI-F and you get the power savings you want and the cores you need for virtualization at a lower cost.
Not sure where you got your number from, in Zurich where I live I just calculated:
A 24/7 running 200W Energy source (which the Mac Pro is I guess) will cost me about 350 CHF / Year ($ to CHF is about 1:1)
My intention here is to build a machine which draws around 50W or - better - less energy.
I just don't feel comfortable having something running all the time and consuming a fair amount of energy when not really needed.
5 years ago someone on this forum - when I asked something about a logged error - said something like his new hardware would payoff in less than a year.
I don't see it all that way - maybe from his point of view the financial payoff is there, but IMO you should consider much more in the calculations and consequences when replacing a running system. things like how much energy was invested in a part at the moment it is laying on your work bench, how much energy will it cost to be cleanly brought to end of life or could it be recycled etc. etc.
Don't get me wrong, I am not just focusing on get the most efficent system here, I just wanted your inputs/thoughts on this matter.
I don't even know for sure if I need a server standing in my room, I could pay for the service, Zurich has built a very affordable fiber net infrastructure we are using, you don't even feel the remote desktoping lag anymore.
I just like the fact, that in case everthing goes down, there is a box physically standing around which holds our stuff (which then will probably not be that important:) ).