Its a good brand, its a reference cooler design so pushes hot air out the back of the case.
See how GTX580SLI eat Crossfire6950 -
http://www.guru3d.com/article/radeon-hd-6950-crossfirex-review/6
Things like the ASUS DirectCUII are triple slot in width, meaning two of them cover your motherboard -
http://www.overclockers.co.uk/showproduct.php?prodid=GX-249-AS&groupid=701&catid=1914&subcat=1812
Thats just truly silly, firstly the review is linked way before drivers have bought the two setups even closer together, secondly, the "big" gaps in the main bar chart are 1 vs 2 6950's, the 580gtx sli is basically 10% ahead, yet costs at £360 card you linked cost
87% more for, best case 25% more, worst case, 0% more, average, 10% more performance.
580gtx's are simply awful cards, no way about it.
Blind test 95% of people wouldn't be able to tell the difference between a computer witha 6950, 6970, 570gtx, 580gtx in it.
Because of the cost, you can get 2x 6950's in the budget, and be basically 50-80% ahead in almost every game, for around a 10% increase in cost.
580gtx is a great card performance wise, but value, its just awful, a 570gtx is infinately better value, £250 though, they were going for £230ish for a while which was even better, anyway, 10-15% less performance 30% less cost, much better value.
The 6970 is equally bad value in comparison with a 6950, the choice should be 6950 or 570gtx.
To the OP, for CPU I'd just go the cheapest quad core phenom 2 £90, overclocking a chip these days, with phenoms will be a case of going into the bios and increasing multiplier, nothing more or less.
You could buy a
http://www.overclockers.co.uk/showproduct.php?prodid=CP-284-AM&groupid=701&catid=6&subcat=1328
dual core, it should unlock into a quad core, again one simple option in the bios, but might not be worth it. Mine was £65 when the quads started at around £110-120, now the gap is smaller so probably isn't worth it.
If you want to get a Bulldozer later on, you can, if you don't, a quad core will be ample for games for at least a couple years.
£90 cpu, £190 for a 6950, save almost £200 from that 580gtx, and if you wanted to your PSU could easily power another 6950, but I wouldn't recommend it.
New AMD gpu's are only a few months away, get a 6950, save a bunch of cash, when the new cards come out, sell the 6950, put the saved cash in, and buy a new card that will be almost twice as fast.
Infact, seriously £360 for a gpu is mental on release, with over a year to go before new gpu's, today, with new gpu's that will absolutely demolish the current gpu's less than 2 months away.
Get something to tide you over, CPU, meh, bulldozer will be faster, but for gaming you don't need that much cpu power so upgrading won't really do anything for you.
But a 6950 to a 7950 is a HUGE upgrade. Save your money, £360 on a 580gtx is about the worst value computer hardware purchase you could make. Phenom prices will come down a bit but won't crash in a couple months, in three months a 580gtx will be worth half as much.
recommending something other than Intel, madness...apparently!