Desktop upgade, CPU/GPU?

[NZtechfreak]

Looking to get some upgrades on the desktop PC, probably end goal is to run GC titles on a 4K monitor. CPU will be i4790K unless someone has a better suggestion (bearing in mind I care about performance, not cost or value proposition), for GPU what should I be looking at? 2x GTX 770 to start with, or go higher discrete card like 780 TI? Probably should add that ill be streaming to my Shield Tablet BTW, so an Nvidia card is a given.