Thanks for the further comments.
At this point it is a choice between the 65" C9 or GZ1000, and I'm certainly still open to the LG - is it the general consensus that the LG is superior in regards to PQ etc over the Panasonic?
Currently the primary external devices are an Amazon Fire TV 4K and 3G ATV; planning on upgrading the latter to an ATV 4K at the point of buying the new TV. TBH I now prefer the convenience of using the TV's built-in apps (if available - at this point our LG LCD has everything bar Kodi and UKTV), given I do like the WebOS interface on this (so, yeah, would be totally happy with the C9 interface).
How much attention should I give HDMI 2.1? I take your point re eARC and use of the TV's own apps (now having read up about it!), but are any of the other improvements offered by 2.1 significant in relation to a TV that has been designed prior to any of these benefits being available?
I can't find any mention re the Panasonic having HDMI 2.1, so assume it's a no on that front; if I can see 2.1 support as being a likely benefit in the future then that's certainly a tick in the pros column for the C9.
LG is the only TV OEM at the time that has implemented HDMI 2.1 in a 2019 4K TV, as far as I know. Given that there are no sources that make use of it at this time, there is no real drive for other OEMs to implement it. Some OEMs have implemented 2.1 features like VRR, eARC, ALLM in HDMI 2.0b equipped TVs, like Samsung, so its not the be-all-and-end-all either. But eventually we will get 4k120 full-fat HDR sources, so you can make use of every last bit of that lovely OLED panel in future. I wouldn't pay a massive premium for it, as again, no way use of it at this time, but it is a big differentiating factor for comp if price is near enough. As you said, a tick in the C9 pros column.
I feel you on the convenience factor; when I see people b*tching about how bad Android TV is, I feel like I have been spoiled by WebOS haha