Onelife - I understand what your saying - but remember that is under test conditions from the link you gave.
Here is a bit of REAL WORLD info....
http://www.overclock.net/ati/471762-...er-supply.html
Guy has a 550W PSU - and he doesn't have the power to run the 4850x2. Everything points to a hefty PS of at LEAST 600W or more. When you start figuring on drives, CPU/Mainboard, additional periphirals - you are looking at cutting your tolerances WAY TO THIN with anything less than 600+. Also remember that you don't want to run the PS at max - your going to blow it out quicker. Better to add in a bit of a safety factor, or the next time you hook up something to a powered usb port, it might just go up in smoke.
Its your build, but you asked for advice.
I am in the US so I can't buy in pounds - but 600 works out to $955 in American Dollars. Now - with that budget - here is the HARDWARE I would purchase to get the best "bang for the buck". (This assumes you are going to use your current case and any Optical Data drive - CD/DVD reader or burner.)
Asus M4A78-EM - $89.99
Phenom II X4 965 Black - $239.00
2X Seagate 750Gb HD's (32MB Cache) 7200rpm - $59.94 Each
Transcend ddr3 1800 4BG kit $159
Corsair TX750W PSU - $120
This totals to $728 - but does NOT include your vid card.
I didn't put it in because you have some choices at this point. We have a hare under $220 left. The Asus is setup for crossfire - but I suggest you avoid it. Instead - your BEST option would be:
ATI 4870 X2 for $199.99
You COULD go with a Nvidia GTX275 for $214 and stay within the budget - but you would be cutting it alot closer and really wouldn't get as good performance.
You could also cut costs on things like the second HD. Drop the second drive, go with the 4870x2 - and the savings cover all the sales tax on top of it.
This is without any OS - but since you indicated you were building that way anyway, no point in buying one.