I’m not so sure about the price difference, but I would agree that (after spending a couple hours digging) that the power consumption difference is not all that great.
It was actually difficult to find some real world stats on a comparable E5 xeon server and its’ power use… but I did come across this article:
http://www.tomshardware.com/reviews/supermicro-6027r-n3rf4-tyan-gn70-k7053-intel-r2208gz4gc,3150-15.html
A quick look, I averaged between their 3 comparisons and the system would consume about 430W (dual xeon e5-2690). If a e5-2665 was used, it would be ~40W lower. So, 390W would be a fair measure of a dual xeon E5-2665 at 100% load.
Compared to my i7-3930k at stock 3.2ghz, at 100% load my system uses on average about ~370W… I don’t overclock, but I can guess using a calculator bumping to 4.5ghz at 1.4vcore increases power consumption by 120W. I used this site calc to guesstimate it:
http://www.extreme.outervision.com/PSUEngine
Overclocking the i7-3930k system to 4.5ghz I think conservatively would raise to use ~450W… I think that is conservative, but I could be wrong.
If we only look at the difference in Watts/hr of 60W:
My house has a 13SEER AC unit, which draws ~5000BTU/hr to cool 100sq. ft.
(http://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized)
What we really want to do, is calculate the required cost to offset the heat produced… so we can take the Wattage difference to find the systems BTU/hr production. This is (at 60W) about 205BTU/hr. My 13SEER unit would need to use ~16W an hour to offset this, or about .04$/day (using an average of .10$ kWh for electricity)
Then we need to add the additional cost for the direct extra power use of the CPU (difference was 60W), which would be ~.15$/day.
So, only ~.19$/day or about 70$ a year more to run the i7-3930k overclocked at 4.5ghz/1.4vcore versus the dual xeon E5-2665… 24/7 at 100% load.
You can pick up dual xeon E5-2665s (3000$) and a mainboard (580$) for lets’ say 3600$… versus the i7 @ about 900$.
Yes, the difference of 2700$ and saving 70$ a year… the ROI on power savings would take 38.5 years.
But, if we look at passmark differences… the i7@4.5ghz seemed to score around 17,818 while the dual xeon scored 18,128. ~2.3% difference
(I had to browse through here to find some posted scores on the overclock: http://forums.overclockers.co.uk/showthread.php?p=22269060 )
However, if you do not overclock the i7 the E5 system produces a 33% difference… power consumption at this point is also negligible.
In the end, putting the extra work required to get a stable overlock on the i7 can be worth the trouble… it just takes some time, know-how, and a bit more $ for a solid cooling solution.
Personally, I’m using an i7-3930k… tis’ great, I dont’ overclock it, and the turbo mode works just fine when I load it up. I think my dumb math here is going to be a little off (especially the BTU/hr to cool my room), but close enough.