Nice! Thanks for the input everyone. I've had my new PC up and running since Friday, and it's a pleasure to use. The graphics are actually too powerful for me - runs TF2 for instance on 100+fps with max settings, so I've ended using VSync for the first time ever.
My final spec differed only slightly to the one I posted last week. I upgraded to the i5 760 for a few pounds more, changed the RAM slightly to match one on the ASUS QVI and switched PSU to Antec TruePower Modular 650W.
Looking forward to playing Civ5 on this!
IMO if your FPS>Hz (monitor refresh rate) then bump the settings,