well... I just pulled the trigger and bought a 4k HDR TV. Upgrading my 8 year old 32 inch TV in the bedroom.
Ordered the Vizio P50-C1 from Costco. I have been gaming on a 40+ms tv for a while now, and haven't really noticed anything. Don't play many multiplayer modes, usually just single player games on consoles. While the lag is around 60ms in HDR right now, they've said the next update will bring it down to around 45. (And anyways, if I get serious about a multiplayer game, I'll probably forgo the HDR for that mode/game and play on the input that has 19ms lag.
Usually don't do returns and what not, but if I do find the lag to be too much or something, or certain features just aren't seeming up to par, Costco has a nice 90 day return policy/period so this doesn't feel risky at all to me.
Also, Black Friday is within 30 days so if there's a sale, I can get the price adjusted. It's currently $90 off anyways and this TV hasn't really gone on sale much if at all.
But yeah, if this TV doesn't work out for some reason, I'll likely wait for next year's models.