Have you tried ZEC? Because from what you are talking, since they aren't balanced (memory/core) like amd and lower nvidia cards, would be interesting to test them on a mining process that requires both memory and core power. Using higher than 8 intensity would be also nice (dunno if this is possible).
Unfortunately I haven't tried ZEC, but according to WhatToMine, gtx1080 should give around 450 H/s for ZEC. It should be profitable to mine it solo, just I don't know of any ZEC dual miner to experiment with