GPUs can handle somewhat high temperatures pretty fine (around 65-80C). I have seen people running their mining rigs at 85C for 3+ years with no problems (R9 290 cards aka heat blowers).
To get the temps. down, just move the hot air out of the room you have your rig in.
yes, R9 series (290,290x,390) can run at that temperature even 90C for 3 days, but
80-90C isn't good for other hardware especially USB Riser can melt (that's what I experienced) and sometimes Rig can restart itself, until now to reduce heat all my Rigs using assembled VPM (Delta), this method pretty good (for me).