Also, because the mini-displayport ports are also only mini-displayport, you can't add an external GPU enclosure to either run SLI 1070's or to double the output count.
What about using a mini display port hub to get the 4th?[/quote]
Mst hubs are great(I have a USB c one for my Thunderbolt port) but you can't go beyond the cards limit. Gtx 10xx range is 4. 3 outputs and one monitor. Amd is 7, that's why the new Mac can do 4 outs. The datapath or matrox route is still the best.