Basically the Intel i5 Haswell processors are suitable for almost every gamer and are the best price/performance rated processors on Intel's side.
The Intel i7 Haswell processors are for multi-purpose, but are still very often used for gaming even if when it is not actually not necessary over an Intel i5 Haswell if It's almost solely going to be used to play games.
If you use other heavy applications, like Autocad or 3D rendering often in general, then I'd say maybe there is a point in getting the i7 over the i5. There are games that benefit from more than 4 threads, from those games you could see an improvement in performance but for now this list of games is very little.
Also, and this quite personal, is that virtual cores are not a good solution for real-time rendering. If you intend to purely play a game that you know supports up to 8 cores/threads, I would definitely recommend the FX-8320 over the i7-4790k.