Mixing/Matching RAM Sizes, Frequencies, ETC.

[SlothPony]

In short, I'm in the market to perform some upgrades to my rig. One area that I know I'm lacking is RAM. I currently have 8GB (which I've always been an advocate for in terms of gaming), but because of my ever-evolving role at work I'm now using up much more than before.

1. If I currently have 2 4GB sticks of RAM in my computer, should I buy an 8GB stick or 2 more 4GB sticks?

2. Are there any numbers I should "look out" for that could cause the new RAM I purchase to be incompatible with my current RAM? I'm going to be purchasing the same frequency (1600MHz). Anything beyond that to be aware of?

3. Any objections to G. SKILL RipJaws? Is there some better RAM I could purchase to add to my rig?

For reference, my specs are:

Core i5 2550k
Samsung 848 Pro 256GB SSD
8GB G.Skill Ripjaws @ 1600MHz
Radeon HD 79790
Gigabyte Z68A-D3H-B3

 

[Tradesman1]

It's not a good idea to mix DRAM, even of the same exact set. Any time you mix sticks it can be problematic, which is why they sell such a wide variety of sets (and why they cost a little more than individual sticks) , in a set all the sticks are tested to work together, the SPD of the sticks is also programmed for the number of sticks in the package to let you use XMP...so in this instance would suggest a 2x8GB set. GSkill is prob the best sticks out there, and for your rig would suggest the 1866 Ripjaws X F3-1866C9D-16GXM or maybe the Snipers in 1866 - F3-1866C9D-16GSR both are great sets with the Z68