Long story short, maybe I went to a little to quick in this but its gonna be fine.
Its been 6 years since my last PC, went mbp's and while I still like their laptop I dont need one anymore and a desktop tower fit my needs better (tired to deal with external hdds/optical drives/etc)
So I build myself a skylake build with the techreport september guide, and went with the intel 750. Meanwhile I was excited as f**k about my new build and started searching deeper into these driver AFTER I buy this (I was aware of the slower boot, but knew nothing about this whole M.2/U.2 thing)
I still believe that the 2.5" with the asus hyperlink m2 adaptor was the proper choice. I think the boot would be on par with any M.2 drives (but I dont swear it) and while I may never go the SLI route, its still now a 100% dead option because im "stealing gpu lanes".
The whole point of the z170 was to bring more dedictated lanes for the m.2, and by going with the add in card, im basically "wasting" them.
Like I said, I dont plan to do any SLI, but if im going to sell this to someone who does SLI in his build, depending on the board, it might not be the best choice.