Should i stay with i5 4690k or get an i7 4790?

Depends on what you're using it for. If your are going to use it for rendering and video editing, you could benefit from upgrading to a 4790k. If it's for gaming, the upgrade isn't worth it. The 4790 usually achieves 2-3 fps over the 4690k in games.
 
If you're thinking of getting the non-k i7, then consider the xeon v3 1231. If you're going for a k series upgrade then 4790k.

Either way, listen to Lag. Upgrade only if you need the extra cores for rendering and what not. Some games might actually get some decent gains from the upgrade, but nothing that's significant.