To answer many of your question.
my build as following.
CPU: AMD Phenom II X6
RAM: 8G
Hard Drive: WD 500G & Samsung 840 SSD 120G
Video Card: Asus Nvidia Geforce GTX 550 Ti
Motherboard: Asus Sabertooth 990FX
I've been trying to upgrade my video card to an AMD to well fit with my CPU. But it's so expensive! The ones that are better than 550 Ti are at least 200 more. and i believe it isn't a huge difference right?
that's why i came across this idea of getting a new CPU for about 180 bucks to see if it would give me a significant upgrade.
By the way, I also play Guild of Wars II. Tera. sometimes. But not that often.
I bought 8gb RAM honestly because I knew I would be using a lot of tabs on one window. It has not been any problem now. It's been fast.