Survey on GPU Card

I'd like to focus on just 2 low cost GPU cards. If you only have $350 max to spend on a GPU card just for Da Vinci Resolve for 1080p, 2.5K, and short 4K work, would you spend it on:

(A) Nvidia GTX 970 4GB
(B) AMD Radeon R9 390 8GB

Please do not suggest Titan, Fury, GTX 980 cards as they do not fall within the said budget. We already know they will perform better and faster. Thanks for participating.

I had some issues with the 970 card slowing down massively when the memory was nearly full.
The R9 390 was faster for resolve, but if you have other software that requires CUDA then it is no use for those programs.

So if it was Resolve only, I'd get the AMD card.

My understanding is the 970 4GB had 3,5 fast RAM, .5GB slow RAM, and when you hit that last .5 RAM...SLOW.

I have a 390 2GB and generally gets by on 1080 with a bit of grading - interested in the 8GB performance so watching...