I've been looking for a way to drive a 40" 4k TV (e.g. Samsung JU7500) as an external monitor for a 2014 rMBP. I know that I can use the included HDMI connector to get 4k @ 30Hz and 4:4:4. But I'd like to drive it at 60Hz. I've seen claims that the signal on the Thunderbolt port can provide 60Hz, but that would limit me to 4K TVs that have DisplayPort inputs, unless I can find a Thunderbolt to HDMI 2.0 adapter. Has anyone seen such a thing?