I priced up a similar spec machine for a colleague at work, and it worked out his quote was pretty much on the nail with Overclockers price, except his was pre-built. I'll find out where he got his from if you like.
Personaly, I've built my last 3 machines from Overclockers, and I highly recomend them. Especially when buying the overclock bundles. If you go that route, try and talk to the tech who's putting your system on the test bench before shipping, he'll give you all sorts of advice on what works best.