Here's a cheap v2 cpu you can get for $20 that's officially on the s2600 cpu compatibility list:Already flashed with 2.0.006, from intel. Need to update with the 2.0.0.e06. I fully expect this to work with v2, but it may be a while until I test that unless someone sends me a couple! As far as I can tell, this is a normal s2600gl/gz system one straight from intel.
Intel CM8063501375902 SR1AY Xeon E5-2603 v2 1.8GHz 10MB L3 Cache LGA 2011 CPU | eBay
You should get one to have one for testing anyway..
Here's the S2600 cpu compatibility list:
Processor Compatibility for Intel® Server Board S2600CP Family and...
I would not try anything outside that list since it might or might not work. I can say for definite 2696 v2 doesn't work with s2600 MB. so based on that experience as well as the fact intel limiting the pcie to 2.0 for non v2 cpu for no real good reason, definitely only use cpu on that list to test compatibility.