As this is going to be a gaming PC, consider going for the best graphics card you can afford & cutting down on the rest - mainly the i7 components, which I reckon is still too expensive for minimal performance gains in games.
12Gb of RAM is not necessary at all - I doubt any game exists that utilises 2-3Gb even. Again aim for the best graphics card(s), rather than a whole lot of RAM that's going to be wasted.
CM Storm Sniper Case click here - cheaper & better quality.
Corsair 750W HX Modular PSU click here - cheaper & will easily run 2x 4890s / 2x other single-core GPU too.
OR, a £93 Antec CP-850 850W Modular PSU click here - but ONLY if sticking with the Antec 1200. It's hard to ignore at ~£40 less than the Corsair 850W HX for essentially the same thing by another quality brand.
Go for a non-eco, faster hard drive. e.g. Samsung SpinPoint F1 HD103UJ click here. Also consider another drive for backups - perhaps the backup drive could be the 'eco' one.
You might want to get a better keyboard too, or a dedicated gaming pad.
You didn't mention an OS, but I guess it's going to be a 64-bit version of Vista/Win7? G