I gave this advice yesterday to someone already:

Get yourself exactly 8GB of DDR3 Ram. Its kinda cheap at the moment in relation to the huge boost on performance you will get on games like BF3. Use 2 x 4 GB Kit (don't buy two single ones, a Kit gives you a higher chance of them being compatible with each other) and set up the necessary 64 Bit System. While playing BF3 you have to run Origin and your Browser for Battlelog as well, so I usually end up using ~ 6 GB of Ram during the game.
Think of your PC like a Bottle and with a powerful CPU and GPU as those you have chosen your RAM will highly limit it like a Bottle Neck.

tl,dr: Upgrading your Ram to 2 x 4 GB DDR3 Ram Kit (Maybe with Intel XMP Profile?) is highly recommended.

As for your HDD: Maybe get an extra SSD as a Boot Device where you install only a few programms who will actually profit from it (again: BF3 loading times reduce drastically). My recommendation here: Samsung SSD 830)

For more information about a gaming PC you might want to read this: So... I want to build a gaming PC. - steamgifts.com/forum

Also: Thanks for your giveaway!

My computer from scratch cost me roughly 800 CAD, not including mouse, keyboard, monitor (I already had those)

For around 2600? You might as well get an i7 extreme lmao, that's WAY more than enough to make a beast gaming rig. I hear AMD made a new series after the 6000 HD series, I believe the 7900 model would a nice graphics card, if you don't like AMD there's always the GTX 500-600 series. If I remember right the best graphics card you can get at the moment is the MARS II, or you can crossfire with AMD GPUs or SLI with NVidia GPUs. Good luck on that build.