Had the same problem back in july.Heat was the issue,and i backed down to 1600mhz on rams,but i set timings to 7-8-7-21-1t@1.65v on my 2000mhz doms.Temps dropped by 5c on cpu,and its now 24/7 fah stable,with no issue`s at all.Qpi/vtt needed 1.56v to be stable at 4000 uncore.Now i only need 1.34v qpi @ 3200 uncore.This is on x58a-ud3r rev2.0 with i7-970 @ 4.2ghz.
Hope its of any help to you,we surely need you to push for top 50.