That's 2x4Gb sticks, and the exact same ram. You can buy that for now, and upgrade it in the future. Very few games are asking for 6GB of RAM on high settings, and those aren't out yet. You can always buy just one 4GB stick or two in the future.
Now the heatsinks on that RAM are big, and got in the way of my phantex cooler. So I took them off (they put them on there REAL good) and it works the exact same.
AMD are coming out with a rebranded 7970 soon, and it's gonna be much faster for a little bit more. Wait on more news for that, I think it was called the R9 290X?
FX 9590 (£240 now, used to be £700)
Here's a great review for it: http://www.hardwarecanucks.com/forum/hardware-canucks-r...
Remember all of that was achieved with a GTX 670.
<>I just remembered this system is for gaming, so scratch that<>
Get the i7-4770k which is around the same price, plus performs better. Especially with faster GPU's, as it wont bottleneck as much.
GPU: Wait for the new AMD cards, otherwise consider a GTX 770, or 680. The 770 is a 680, and if you get a 680 you can replace it for an 880. The 880 is going to be brand new architecture, unlike what the 770 was or the new AMD gpu's are going to be. (Both are rebrands).
Storage: I'd recommend a 128GB SSD minimum, with sleep mode etc on W7 it takes well over 20GB. Plus you'll want to put a game or two you commonly play on there.
I'd also recommend a 1-2TB HDD, however don't expect to be able to install most games or programs on it flawlessly, for example I couldn't get mods like DayZ to update on my HDD, and had to move it to my SSD.
RAM: 8GB kits have become the norm, you find them cheaper than some 6GB kits because of availability. Go for 1300-1600 mhz.
Then make sure you buy from a reputable brand, and that its 80+ certificate is legit. You can check this on the 80+ website.
For case you don't need something big, a Haf 912 will fit you fine. There are others, but so many to list I'll let you do your own research.
Motherboard: For this I recommend something with two GPU slots, so if you don't have enough for a new GPU that runs twice as fast as yours, you can simply buy another one of yours (the price of which will decrease over the years).
That's the majority covered really, I'm giving vague answers because I can't list every product of the top of my head sorry.