I would get the Phenom X4 not the Bulldozer, and I would get a 500gb Seagate Barracuda, with a 6870 GPU, and that would get the price to £612.
So forget what I was saying about the 600W for the 6870, the configurator was playing tricks on me.
As I said, you do not need the AM3 so you can get the price to £612 with the HD6870. You will be fine for the future aswell with the standard mobo in that configurator, for many years
However, I have found how the website was "playing tricks on me". With the 6870 card and the standard mobo, you will need 600W; however if you go for the 6870 & AM3, you only need a 450W. This means that going with the AM3 is actually cheaper, by £10, than without it! (due to the power supply)
But, the cheapest you can get if you want a 6870 and the rest of that build, is £632. Therefore you should get the 6850 in my opinion, since the performance difference is very little between those two graphics cards.
I hope this made some sense! (you may want to read my previous post aswell if you haven't done so)