Also for those using an AV, such as the newer Yamahas, make sure you set it to mode 1. (For HDR) - Default is Mode 2. For others check the manual or search online.
See
http://faq.yamaha.com/us/en/article/..._u/11032/9451/
Worth a mention...
Edit....
One downside to using the V6 4k settings only is that the subtitles look softer. Compared to the 1080's crisper sharper looking subtitles. If you rely on subtitles it is quite a big thing.