Looking At Upgrading Ram, Suggestions Please

[Titler]

Been a while since I did this, so a quick check on my assumptions would be helpful, thank you. I've two RAM slots free in the following system.

* Processor (CPU)
Intel® Core™i5 Quad Core Processor i5-4690 (3.5GHz) 6MB Cache

* Motherboard
ASUS® Z97-P: ATX, LG1150, USB 3.0, SATA 6GBs

* Memory (RAM)
8GB HyperX BEAST DUAL-DDR3 2133MHz X.M.P (2 x 4GB)

I'm thinking of adding more HyperX Beast at the same speed. Do I need to add 2 more 4gb, or can I either go for a single stick at 8gb in one of the other slots, or symmetrical larger RAM (say 2x 8gb) without performance issues?

Thanks!

 

[CountMike]

As long as sticks have all other parameters same, size of sticks will not make any difference.

 

[Titler]

As long as sticks have all other parameters same, size of sticks will not make any difference.

Thank you for the answer; if this is the case, it'll come down to which sticks of greatest size I can get cheapest then, rather that worrying about filling both slots... handy!