That Intel board only will run 1333 memory for some reason with the e5-2670 CPUs.
I tried running faster with some 1866 memory and no go. I forget why, but the thread at [H] said why, but I am not going to go look right now. I think I tried my Asus board too and no go, 1333 was all she wrote.
I never ran matched pair, in my dual lga 1366 I even ran a e5620 and an e5645 together with no problems at all.
Ran x5650 with a x5660 and they ran fine, running SMP it ran at the lower CPU speed.
Work units that were one core per one work unit the CPUs ran at their rated speed.
I did not try to mix an E series with a X series, I won't try it either!!