Well I have my GEIL Ultra stuff running on 2.1v @ 4-4-4-12, at >800MHz - but it seemed to suddenly work on these settings, having initially not wanted to play ball ! When my system is running at 3.2GHz (356x9), the RAM is at 890MHz and I give it 2.2v to assist stability, but for 24/7 use I have now scaled back to 3GHz (333*9) and the RAM sits on 2.1v @ 833MHZ @ 4-4-4-12 without issue