So got home, popped the videos on USB stick and tried my two TVs
Samsung 40KU6400 - Supports HDR, but it's largely 'faux HDR'.. however a little improvement on the youtube stream, namely due to less compression, but at least you can see a bit more 'subtle' lighting effects on the the cars and a crispness to the image that is quite nice - 7/10
LG OLED55C6 - More like it! This TV supports better HDR (still not the full standard) but it's more than enough to make a nice 'leap' in the lighting, the extra contrast etc really add even more subtle lighting to the paintwork that actually do somewhat address more of issues I saw, namely the back of the car looked lifeless, and the scenery looks great in motion, really really crisp with so much detail. The skies at the end of the Nurb GP track is great, awesome reflections in the puddles, and the skies in both videos look great.
I'm actually worried that the SDR captured videos which we've seen most of (that where taken with the console correctly set to SDR) really do make the game look a bit dull and there is a whole 'layer' of subtle lighting that is missing, leading to a very boring looking game. I wonder if they are concentrating too much on HDR and really they need to re-profile their lighting to give a similar contrast and subtlety to the reflected light, or it's going to look a bit lifeless to a lot of people and not come accross that well in 'comparisons'..
Overall, nice though, the only 2 areas that needed improvement where the GT-R's interior looks so flat it hurts, and the wobbly wipers again, both fixable.. Everything else I'd leave as-is, you don't notice all the other shadow nitpicks when actually playing so I am OK with the other compromises that show up in static comparisons.
I'm so glad I got the LG now, it's on sale in the UK, effectively only £1350 with a 5 year warranty which made me jump in.. of course I will now have to upgrade my sim rig to something HDR/Freesync 2 etc.. hopefully by november something 28-32" with HDR10 capability and freesync 2 @ 4K will be along..