Maybe it's just me but I've been a happy camper with these
KB 128gb 1066x cards that I've been using on my 5D3 the past several months.
I can get continuous 24,25p 1080p in MLV w sound.
30p with slightly less resolution ( 1920x1038 ) to get continuous in MLV w sound. (otherwise I can push it to 2-3 minutes (about 2200-2500+ frames) before dropped frames @ full 1080p)
This was all done with HaCKeD preview enabled.
Also be sure your cards are in exFAT!
