After some quick testing (only some CB runs) my 1660v3 (8core xeon variant of the 5960x) @ 4ghz CPU and cache with 2400 CL 10 is delivering nearly the same numbers like my 4,5 ghz 1680v2 2600 cl11 is doing even at something like cb15 (no avx/2).For X79 E5 1680 V2's are unlocked 8 core Xeons. I have two of them. Their performance is nearly identical to a X99 5960X when both are overclocked to the same speed (4.5GHz for mine). The 2697 V2's have four more cores but are also locked.
Clock for clock (only did some runs since my cooling is not set up) i saw a uplift about 15 - 20 %.