Welcome back - also been awhile for me, although I pop in and read up the latest once in a while without logging in.
Anyway thought I'd share as I've found myself in a similar position as you. Had a 4K TV for awhile but couldn't be bothered to upgrade my AVR to 4K because I was happy with the sound from my old one and don't have much actual 4K signal anyway. Long story short I bought a new Onkyo TX-RZ820 during a huge boxing week sale. Results? Meh. I like that it has updated connectivity and control and 4k from my previous Pioneer Elite, BUT it is not an improvement in sound quality, not worse either, just different. So in the end my life lesson on this is to consider a step up in all areas and not 'just' a lateral move to support the new format.
Hindsight says I should have gone with Anthem, but I didn't have the $$ for that. Everyone I've spoken with raves about the Anthem AVR's, including a few people on this forum I've also exchanged messages with. Unless something else comes along, that'll eventually be my next move. The dream being the Anthem AVM with separate Axiom ADA amplification.