RAM Question

Dual Channel is better than Single Channel.

Just download it http://www.downloadmoreram.com/

Just get four ram sticks if possible and have 16 GB of RAM.

download some more

Do you have dual, triple or quadruple channel memory? Anyway get a kit of 8GB capacity or 16 for whichever channel your mobo has, rather than mixing different spec of RAM modules because you can literally fry your RAM if you mix them and in best case scenario your new RAM module will be throttled back if it is mixed with old one, try to avoid that. 8GB should pretty cheap nowadays, but then again depending on your mobo's channel. Also check what MHz and voltage your mobo/cpu supports and according to that find the one with great balance in a way of lowest timing/highest MHz, because going for best latency and low MHz and vice-versa is actually slower than the low timing/high MHz solution.
Man, one can type books for all the things about RAM, if you're not careful you might regret it, take care picking RAM and check some reviews/boards that have similar setup as your PC, good luck!

EDIT: Right to point out voltage note, if your mobo/cpu supports 1.5v RAM, buying 1.65v ram and using it on 1.5v rated mobo/cpu will give you more work to do, undervolting module in BIOS so it will make slower timings or lower MHz (bandwidth/frequency in other words) and it can even void your warranty, again take care picking it.
EDIT2: Someone can correct me freely if I'm wrong somewhere.