Wattage for 390 oc.

The Antec High Current Gamer is a good quality unit made by Seasonic. It has enough power for your system with some overclocking. The 4790K will turbo to 4.4Ghz. without overclock so I'd leave it alone and work on the R9 390 to try and squeeze a bit more from it.
 


Even when doing oc to the cpu and the gpu at the same time?

I would like to plug at least some usb stick without a power leak xd.