My C9 arrived yesterday, wonderfully everything has gone smoothly.
It's a really easy TV to setup, and pleasingly there's no LG account to log in sitting over the top of it like on my old Samsung KS7000.
Picture quality is superb. I've not tried to tweak the settings at all, just turned off the usual TruMotion stuff and used the Cinema preset. Once the firmware and all the apps updated everything worked as I'd hoped, sending through the expected signals, Dolby Vision and Atmos in the relevant places. Annoyingly AppleTV+ doesn't appear to offer Atmos on it but it seems like they restrict that just to Apple Devices anyway.
It's working perfectly with my AVR the x2600h. Once it got past the initial CEC pairing issues you always seem to get it worked just as I'd want. Also no lip-sync issues which some threads on here suggested there might be.
Really impressed by the software and the magic remote, definitely glad I went with that over getting the Panasonic and having to deal with its poor software.
So if anyone else over the next few months finds themselves asking the question that caused me to start this thread my recommendation is get a C9 without hesitation.