Thanks =) I've been looking a little more (and my budget has gone up a little, woo!), and I've had my eye on the Alienware X51. As I'd like it to last, I've been thinking about going with -
Intel® Core™ i7-3770 (3.40GHz, 8MB L3 Cache, 4C)
1GB GDDR5 NVIDIA® GeForce® GTX 555.
8192MB (2x4GB) 1600MHz DDR3 Dual Channel Memory
I'm not intending this to be a colossal beast of a PC - I can't afford that. But as far as I can tell, I ought to be able to play pretty well with those specs. Hopefully ordering it within the next week or so, possibly trying to get into the last beta.