Nothing wrong with th i7 at all, but if you want to use this for gaming you can better consider choosing for a ATI Radeon 6800/7800 series or nVidia GeForce GTX 660/660 Ti (660 Ti with no more than 1.5 GB of graphics memory due to cut memory ).
It's all up to you which brand you prefer as I don't want to start one of these 'nVidia vs AMD' fights, just watch some reviews and tests on those GPUs, they all have their strong and weak sides.
http://www.tomshardware.co.uk/gaming-graphics-card-revi... there we go. i'd be looking at things from the 6th tier upwards depending on what resolution & detail settings you wish to game at. the 7850 1gb & 7870 seem to be the price performance champions right now (as far as single screen gaming goes) but for resolutions beyond 1920x1080 i'd probably be eyeing up a gtx 670 or better, especially if i was using a trio of monitors.
The intel hd graphics on the cpu will more than likely outperform the graphics card.
If you own a prebuilt and are considering upgrading save get something a little more current. You will need a power supply as well.