850watt psu for 2 gtx980 and 1 780ti doable ? (with a i7-3770 which doesn't use lots of power)
Yes 165Watt x 2 = 330 watt for 2 980 + 250 watt 780ti = 580 watt .
plus the cpu and the rest of the system, adding to roughly 110W (to be safe), allow for gpu self and manual overclocking, 40w
total = 730w
850w @ 90% eff = 765w (psu efficiency often gets lower the closer to maximum you get)
~spare = 35w
just be careful djm, it may be a good idea to put a kill-a-watt meter on the system if you have one, then add one 980, then another and just see how close they get running some benchmarks each time