No, I've been mining on and off since 2012. I still use ribbon cables on one of my rigs and they work great, fyi.
The 1080TI loves more power, and the gain in hashrate on core intensive algorithms from running with full OC at 120% far outweighs the additional power cost, unless you're paying over $0.30/kwh. Undervolting *is* used by the eth mining community, and those mining memory intensive algorithms, but that's quite frankly a complete waste on a 1080ti...its a core beast.
Not sure if yall are new to mining but undervolting is not considered crippling the card in mining when you have power usuage to consider. Also, are you sure 300 watts on each 1080ti is accurate, nor,ally its like, 180 to 200 watts.
Finally, Ive never seen a build where a card with 2 connectors on top werent run off a single pcie using a splitter from pcie to two 6+2 plug, thats how all 46 of my 1070ti are wired, of course Im not running at 300watts a card.
In the reddit post about octomimer mobo, they guy from company posted a link to the 1080ti models they were testing 8 of and he was supposed to temperature results. I know he said since the board uses mobile cpu and ram, it only draw like 40 watts so almost all your 2200 watts is available for cards. Hope that helps