Mixed ram sizes in slots.. help pls

[Old Man]

I have 4 slots on my motherboard with 2 slots having 2x4gb leaving 2 slots free, so my question is if would be fine with filling the other 2 slots with 2x8gb sticks?
(all ram will be the same type: CMK8GX4M2A2666C16).

TY in advance

 

[8 Pack]

Probably not. But try it if you have nothing to lose.... Different density often not playing well together

 

[P4Clock]

That would depent on the motherboard in question, however i have never had a problem running different size sticks. you must see what set as the slower timing and use that in channel one.