You're absolutely right Jennifive. Choose what makes most sense from a performance vs price perspective. I was in the same situation as you a few months ago. The 1070 were selling for £350, the 1080 for £380, the 1080Ti for £700... lol.
I went for 5x1080, logically.
1080 is not good for ETH.
There are 1000 other coins out there.
@Vann: RX 570 is the king of profitability as long as you mine EThash or Cryptonight.
If you can't get them, or want to mine anything else, the 1080 is a great GPU.