Hi, the new imac 5k is going to arrive in a few days, I've gotten the stock 8gb as i intend to upgrade it myself. is it safe to use 2x8gb ram modules I bought via macsales for my mbp? the only difference i see are the Mhz. if this works, should i order another 2x8gb, since I'd have 1600mhz modules in the imac, should I buy two more identical ram sticks or mix-match with the 1867Mhz OWC offers for the imac? thank you very much!