Which PC Upgrade?

[puffello1]

I'm building a PC and my budget has increased. I now how 2500$, mind you these are Canadian funds so prices are higher than American. With this 200$ dollar increase I can either upgrade my motherboard to an x99 deluxe from an x99-a II, upgrade the cpu from a 5820k to a 5930k, or I can upgrade from a GTX 1070 to a 1080. This computer is for gaming. I could also keep saving up for a 4k monitor... So please give me your opinions on this matter.

 

[CTurbo]

GTX1070 to 1080 would make the biggest impact

 

[puffello1]

GTX1070 to 1080 would make the biggest impact

Any suggestions on which gtx 1080? Must be around 900$ CAD.

 

[puffello1]

Gigabyte gtx 1080 windforce vs pny founders edition ?

 

[puffello1]

If I were to upgrade to gtx 1080 I have found that the asus rog strix a8g is in stock and price range. It has slightly lower clock speed than the asus rog strix o8g. Is it any good?