Well, GTX1080 is good for few coins, bad for the others. I would go with 5x GTX1070, as the difference between 1070 and 1080 in mining isn't much, thus having an additional one would give you better hashrates. You can also have a look at this:
https://bitcointalk.org/index.php?topic=1768510.0 thanks, interesting info.
interesting how much can raise gtx1080 by NiceHash.
now testing gtx1070. average - 4.3 - 5.3$ per day.