If you have 64 bit Operating System you can add more yours can have 32 GB if you want to get the best go to the Gigabyte website and look up your motherboard. It should tell you which ones are supported. If you want to get more ram but are on a budget then go for standard DDR3 ram. I bought standard and gaming ram just to find out gaming ram is no different in speed just a name, price, and looks.
It really depends on what you're doing. 8GB is more than enough for almost anything. Media editing, RAM disks, and running multiple Virtual Machines at the same time are just about the only reasons for more than 8GB.
Also, 1600 is the sweet spot and there'll be virtually no real world gains from anything faster. RAM related benchmarks will show the difference and it will help with RAM disk speed, but you'll never "feel" the difference otherwise.