He's looking to get higher numbers in fps, whilst CPU will help render things faster. I would not solely recommend him spend good money on a CPU and RAM if he's trying to achieve high FPS.

A Balance between the two is what he needs.

Maybe a Fx-6300 CPU with a GTX 750 ti is a good combo.

Obviously it's crucial he has 8 GB of RAM though, otherwise his game will crash a lot more.