I got a MBP 2015 but I cannot get 60hz on my Dell UP2414Q (and Yes, I enabled DP1.2), anyone got any idea?
I don't know the answer but am interested also. It looks like you can get UHD at 3840x2160 and not 4096x2160. The hd 6100 specs show 3840x2160 at 60hz. I hope the mbr 13 can go to 4092.