You don't need an i7 though, an i5 is a lot cheaper, and in the vast majority of games offers the same gaming performance.
Would you be overclocking? If you're not you could get the Haswell Xeon which is an i7, but at the i5 4670k's price.
For 900 pound, it's very likely that an i5 4670K and Radeon 7950 will be the way to go.