We are recommending against 4k until technology catches up with it.
a) There are no Hi-Refresh rate 4k monitors because, though we have had Display Port 1.4 compliant GFX cards now, there are no capable DP1.4 monitors ... there's not even a DP 1.4 cable available that I have seen.
b) If you are an avid gamer who wants to be > 60 fps in their fav games, there is no GFX card that can deliver it. Even twin 1080s in SLI can't manage 60 fps in all the games at 4k in TPUs test suite. As to the 1070 ... refeernce card performance below, AIBs are a bit faster.
Anno 2205 = 36.8 fps
AC Syndicate = 43.2
BF3 = 57
BF4 = 42.1
Witcher 3 = 35.2
WoW = 100.7
BM AK = 48.9
COD Black Ops - 28.9
Crysis 3 = 27.8
Fallout 4 = 58.7
FC Primal = 33.1
GTAV = 38.2
Hitman = 29.3
Just Cause = 40.7
Rainbow 6 Siege = 50.6
RoTR = 32.4
c) Folks generally keep their monitors much longer than their systems. To invest in 4k now, methinks, is a bit scary as once DP 1.4 capable panels arrive, the value of no DP 1.4 panels wll drop in the toilet and be extremely difficult to sell