Gang,
I’m using 770gtx overclocked cards for rendering and development with Unreal4. Is better if I switch to K series cards, or just pickup the 980’s that were just released…
Go with the 980, the K-series (quadro) are more for advanced 3d simulations that are not used in games currently (like rendering for move type CGI). The 980 is a gaming card, and since UE4 is a game engine, it will work great! I plan to pick one up as well (I have a 660 ti still), super happy with the price of the 980! 
Kool, I’ve tried with K serious in a laptop, I wasn’t impressed, also played with the workstation version which didn’t impress me with Unreal either… so thanks for the validation…
No worries!
Only thing I would add is that you probably wont see a huge performance increase, it will be a good amount, but I have been reading online that anyone with a 770 or greater might benefit more from the next series coming next year, but that was advise for the public really, in game dev the more power you have, the faster you work, so it is up to you when to upgrade, I am feeling the same way right now though, really want the new 980 it looks awesome! (^^ anyone reading that is looking for a b-day gift for me, you would instantly become my BFF! 
)
Just make sure to send it to me first, so I can make sure it works right
i would go for a 970 with 3rd party cooler, seems they offer a good overclock and it will give access to the new GI system without making your bank manager cry.
780 TI, Almost a titan for half the price. Though i’m probably going to get a 980 soon. 