check if the one u have now is 1.5 or 1.35, mm2012 can use either but try not to mix them. I would say to get at least the same voltage/speed if you can't get the same brand/make/batch.
I am using the Kingston HyperX 1.35v 1600mhz cl9, this is so far the fastest rams i can find for mm2012.
1866mhz rams run on the mm2012 as 1600mhz.