I am on the same idea, go for a new processor and would keep that 970 its still a pretty good damn card for the price right now and u wont loose money anymore with it, its at its lowest right now. I would personally try to find a 970 in the same model and sli it for now. U can get one for like 150$ just test it! u wont loose!
I mean it depends on the game u want to play but a 970 sli will ride u a long way again for very cheap.
Its the perfect time to find a really really cheap one, im not sure if the game u play will gain from SLI, but personally, my 980ti SLI is working flawlessly for what i play... do your homework! haha
I tell u by experience, sell that motherboard and processor. I had the same cpu as u and asus rampage mobo, sold it for like 400$ on Ebay then Buy a i5-k or i7k and sli that 970 and OC and Test it why not?!! for 150$ i would do it. Just resell it 150$ if its not working good for you or Sell both for 300$!
do your test yourself and enjoy u have nothing to loose, if u manage to get good performance with the sli u just saved 100-150$, and later u will see... u wont loose money anyway in all this!
U can get at least 200$ for your current CPU+MOBO on ebay.
i would Consider these for the price right now :
-Intel Core i7-6800K 350$
-ASRock X99 Extreme3 LGA 2011-v3 (not this model in particular) but its like enough and its 140$
-DDR4 memory (the less expensive of all it does not matter really.)
So! My opinion is firm haha! i would start with the basement! the cpu for now and for futur!
Look!: if u had an i5 Devil Canyon, i would go for a GPU but your CPU is way too down the ladder to start upgrading somewhere else... build a strong basement for now, u cant go wrong with this CPU for the price and its time to sell your rig or soon nobody would want it... if u don't have enough money to upgrade sell your rig and get that 200-300$ back right now! Because later u will start from scratch because u will have nothing worth to sell.