Myricom w/ Sierra -> High Sierra
Had to reinstall driver from website (old according to date, nothing changed), reboot, card worked again.
SmallTree drivers together with hacked Intel x520 or x540 cards (Dell or original Intel) are working fine with High Sierra. By the way AMD 570/580 are also natively supported by High Sierra. Feels like a better Mac now. Everything just working after upgrading to High Sierra. Less hacking.