Best video card for Bitcoin mining

Hey guys,I'm trying to determine how much of an upgrade would some new RAM be for this build (especially with the low prices of RAM these days). It's a computer I built around Christmas time using mainly parts from a previous build and only upgrading the CPU/Motherboard on which I got a very good bundle deal directly from Intel (I know it's overkill for what I do, but I paid 250$ for both...) and then upgrading the video card as well. I didn't have time to look into upgrading the rest of the build until now and I wanted to start with the RAM.

Build:

Motherboard: Intel DX58SO with Four 240-pin DDR3 SDRAM Dual Inline Memory Module (DIMM) sockets, Support for DDR3 1600 MHz, DDR3 1333 MHz, DDR3 1066 MHz
CPU: Intel Core i7-970 @3.2GHz
Video card: Sapphire ATI Radeon HD 5870
Memory: 2x Patriot Memory 1333LL Series 2 GB DDR3-1066 DDR3 SDRAM (7-7-7-20 @ 533 MHz) (6-6-6-18 @ 457 MHz)

I can give more info on the build if it's needed.

Everything is currently at stock speed. As you can see, that RAM is getting old, as I've had it for about 3 years now I think from the previous build. As I really don't know much about RAM, I'm trying to find out what kind of performance increase (as in how exactly would it affect performance) I could get from getting some new RAM. That computer is mostly being used for gaming; the games I play include a lot of MMOs (I tend to download most of the free-trials), Starcraft 2, Battlefield 2 and soon BF3.

So is it worth upgrading at all? And if so, what kind of RAM would be worth getting? I live in Canada so if possible please use canadian websites to link any possible good buy (as in newegg.ca and not .com). Thanks!

Any advice is welcome!

Thank you all for your time!

Edit: I should've mentioned that one of the reason I thought of upgrading the RAM is I'm pretty much at full capacity (3.9 GB used on 4) with SC2 open, iTunes + 3-4 tabs of Chrome. Thanks for the first 3 comments, looks like upgrading the RAM speed won't change much, I might just look for any 6GB triple channel setup just to not get maxed out with just those 3 things open