I have three. I used one of the original Seikis that came out ($500), then I got a samsung (don't remember the model) and that is probably my favorite, and the same TCL you have. I think the TCL is my least favorite.
Rtings does highlight how much difference there is, but even the TVS that are a couple steps up from the TCL are only a couple hundred more, so the cost per unit of screen real estate is still pretty good.
I think the 8ks will have such significantly better pixel density (because it's not like I'm going to use an 86" monitor for 8k, rather a 60" and have about 50% more pixel density). Maybe even a 50-55".