I would get the largest TV you can afford.

I would, also!

I did not follow the rule. To me, it's all about the overall balance. We wanted a larger T.V. to fit in this alcove. The cabinet is just a tiny bit smaller than the T.V. I think that the chairs help the balance.

You could also get the smaller TV, and make your own frame to make it bigger and more attractive.

77" is the current expensive but doable size in LG oled. About 1800. No need to put furniture under it.

The larger one and mount it a few inches higher.

Agree that it needs to be a few inches higher. Not sure how far away you will be viewing it, but I lean toward larger.