The 950 is a lot cheaper and performs a lot better than the 960.
Reviews : http://www.overclock3d.net/reviews/cpu_mainboard/intel_core_i7-950_review/1
Plus, it overclocks like a charm. It is possible to run it at only 1v at stock settings, which is really impressivee !
It's also quite easy to reach the 4GHz with a bclk of 200MHz and a multiplier of 20. It's highest muliplier is 23 (without TurboBoost, with it, it might jump to 24), which means that you can very easily obtain 4.6GHz without changing the bclk.
Hope this helped,