The biggest thing is if the sticks will even play together and there are no guarantees, not if with two packages of the same exact model of DRAM - that's why the manufacturers make offer such a wide selection of packaging 1, 2, 3, 4, 6 or 8 sticks, all the sticks in a package have been tested to play nice with each other. We often see people 'outsmarting' the manufacturers and buying two sets of 2 sticks rathen than a 4 stick set, because they are 'saving' $5 or whatever. Only to find the two sets won't play nice, and they they pat return postage, restocking fees, ets and that $5 they 'saved' ends up costing them and extra $20-25 or more 😉 The forums are full of threads about people trying to mix DRAM.
If you already have the...