I just recently got a GTX580 to upgrade from my GTX295 and it did make a big difference for me running 5 x instances on a 2560x1600 screen. This would be a similar upgrade for you, and possibly more, so I would consider upgrading your video if you can afford it.

The specs for the system look good, the True cooler that is in the package is more than capable of having that CPU run at 4GHz. Personally I never found much added performance running my 920 overclocked to 4GHz for WoW, but it is something that is so easy and safe to do with these processors, you would almost be crazy not to.

The only word of caution is that sometimes having 12G of RAM in 6 modules makes the overclocking a little trickier If the system is going to come factory overclocked, Check this with them first. Given the improvements with the newer i7s over my C0 920 though, I am sure it would still be a piece of cake.