Upgrading from 8gb to 16gb ram compatibility issues

[burgasfanbg]

Hello i was wondering if anyone could help me with the problem im currently having.
I currently have an asrock anniversary z-97 mobo with 2x4gb kingston hyperx savage 1600 mhz ram sticks on it. I wish to upgrade to 16gb and i was wondering if i should get 2x4gb or 1x8gb of the same stick, which is best and are they even compatible?

 

[clutchc]

Best to try to match what you have now for best stability. Plus, a single 8GB stick will put that stick in single channel mode for a small performance hit.