I wouldn't use the 1080's but rather the 1070's... You can pull about 420 S/s per card for zcash and for a 6 card rig you could get the wattage down to about 1000 in total if you configure it properly. ROI on one of these rigs would be 6-8 months dependent upon price but at least you can purchase all of the parts anytime you wish unlike with Baikal right now.
I concur - 1070's are the sweet spot for power/hash/cost efficiency today; with only one except. AMD RX470/480 beat the 1070 for ETH/ETC ... 1070's win for pretty much every other GPU algo.
Mining4Bacon
The recent major price drop on the 1080 has thrown that into question on a few coins.
But neither is going to be worth pointing at DASH given the much higher profitability they both achieve on other stuff.