mix match

[TTesla]

Hi

can I mix two 4gb sticks with two 8 gb sticks?

4670k with ud3h z87

both at 1600mhz

[Volbet]

You can, but it's not recommended. You might run into stability issues, but it can run. 

[bartekxx12]

Yes you can, I am currently running a Corsair Vengeance 1866MHz 4GB Stick, a Corsair Vengeance 1600MHz 4GB Stick, and 2 Samsung 2GB 1333MHz sticks, all running at 1866MHz (1.725V) and passed 24 hours of Prime.