I would wait a little bit longer. Ashes of the Singularity is only one single benchmark with an unfinished game and drivers which are with some certainty still work in progress. Also look at the results in DX11 when considering an AMD-GPU. This is an extreme case, however, AMD does have some problems regarding performance with DX11 compared to Nvidia which you will notice in some games. They get less pronounced, once you crank up the resolution, but there are some cases, where the GTX 970 is quite a bit faster and also deliveres better frametimes then, say, that R9 390 you mentioned. In most cases, the amount of memory is also not really a problem with games right now, not even with the GTX 970's messed-up memory interface - I checked, more than once and practically do so every day. There's some games like Assassin's Creed: Unity, GTA5, and some others, in which you might get better frametimes from 1440p and up or the image quality get's reduced if you have not enough memory (that's happening with the GTX 970 in ACU in 1440p and above for example). However, both the R9 390 and GTX 970 would be struggeling to get decent frametimes (and framerates) in this configuration in the first place. 4 GiByte might be not enough in the upcoming future, but in most cases it's good enough today.
Grabbing a R9 390 might still be worth it, paticullarly when there's more and conclusive evidence that with DX12, AMD can get rid of their performance-problems and driver-related issues. There are some games not too far away that might hint at that, Ark: Survival Evolved will get a DX12-Port in the near future (it's delayed already), which might show some very interesting results. Also, Hitman is coming with DX 12 december 8th, shortly after Deus Ex Mankind Devided will be released with DX12 as well. There probably also will be some more demos and stuff and Ashes of the Singularity should get to a more refined state and also the drivers will - I would expect the performance of the Nvidia-GPUs to increase, probably more so than the AMD ones. Nvidia just can't stand to be less fast, they will make hell freeze over to get in front again - they even might try to cheat a little bit, if they can't do so otherwise.
The GTX 970 is also still selling well, you could with some certainty wait a little bit longer without losing any money - particullarly if you put it in regard with the R9 390, which I would rather expect to drop in price.
Also: Hi
