[noggin]

I've also just checked my 2160/59.94p HEVC clip of a BBC UHD test signal recorded off-air from the 2014 BBC UHD DVB-T2 trial.

I ran it at 2160/60p and then at 1080/60p output resolutions (*)

At 2160/60p output it looked very clean and you could see detail into the very finest grating of the test chart. (These are not pixel-based but are frequency-gratings so you don't get a clean white pixel/black pixel)
At 1080/60p output you could clearly see downsampling artefacts on the frequency grating of the chart.

I'm pretty confident that at 2160/59.94p I'm getting clean UHD replay. Test video also looks very clean and sharper than 1080i or 1080p.

(*) To force 2160p content to play at 1080p over a 2160p connection takes a bit of tweaking. You have to disable "adjust refresh rate" to off when playing back 1080p into a 2160p display, if you don't I think it tries to help and outputs it as 2160p again, but it gets confused and displays a 1920x1080 downscaled image top right in a 3840x2160 frame...

(I don't feel comfortable sharing the test signal as I know it is a copyright image.)