390 for 4k is not enough dual 390's yes. The issues are usually black screen and flickering on some games.But new driver fixed that.I put one on my wifes rig its performing a bit better than 970 in most games. Make sure you have a strong psu and if you have a 600w psu make sure its gold certified or it will start to shut down if you go with the 390.Personally i liked nvidia cards for their efficiency and more optimized titles but usually the gameworks titles even with 980 its had to maintain a steady 60 and i mostly disable gameworks anyways.Also with nvidia playing dirty with performance degradation on drivers to promote 900 series and the 3.5 gb fiasco with the 970 i won't buy their products again till they fix their products. Id say if you don't care about efficiency and just raw power go for 390 since the 970 will tank at 1400p.