Ok so I've decided to check out some custom built options. I'm looking at this site at the moment:
Dude, buy the freakin' PC. The one you were going to buy, the alienware one. That's perfect. It's great. Nothing is wrong with it. You will love it. Stop worrying about it.
They don't. The main thing I'm worried about is motherboard/power/cooling/fans because I have no idea about any of those.
Everything in that alienware PC is taken care of. The CPU comes with it's own heatsink, and alienware will have already installed that, since that's part of the "prebuilt". All fans are already in the case, everything is done for you, you don't have to worry about it.
Well, OK. Still comfortably under £1700 so it's cool. What about liquid cooling? It's only like £50.
Liquid cooling is not necessary unless you are looking for some really, really unnecessarily hardcore overclocking. I overclock quite liberally, and I'm running on pure air cooling, with great temperatures and performance.
I don't really intend to overclock or anything.
If you are going for the i7 920 (which you should, it's the best CPU on the market excluding the new i9 procs, and it's value is unmatched), you will want to overclock it eventually. But, it is so easy to do so, and you don't have to even increase the voltage.
Go with the alienware computer. I highly recommend you don't use these other sites you're looking at. Seriously.