I'm surprised you only managed 212HTT. Are the memory modules matched pairs? If they are two sets of matched pairs have you tried each pair individually?
Also try relaxing the memory timings, at speeds over 230 my four modules at 3,4,4,8 are good to about 270HTT. Separately one pair are good to 305HTT and the other to 270-275 at these timings and 2.8V.
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