Outside of benchmarking scenarios you wouldn't notice a significant difference from the i5-2320 to the 4670k. The same goes for the i7-4790. Unless you're running applications for video or photo editing or are chasing high benchmark scores it's not worth it to swap out your CPU + motherboard.
You'd notice a greater improvement in games if you upgraded your GPU to a GTX 770 or 780.
In terms of CPU's, I'd sit this generation out if I were you.