Hi OP, I've got a 65" SONY BRAVIA X900F connected direct via HDMI to HDMI. Works perfectly. After connecting, I open System Preferences > Displays > Scaled .... Here (if you're looking at the 4 pics) I choose the 2nd from the left.
If you like you can hold down "option" then click on the word "scaled" and it'll give you the various resolutions. So 2nd from left is "Looks like 1920 x 1080." If you choose 3840 x 2160 the text will look too small. The "Looks like 1920 x 1080 is very easily readable on a 65" and text is sharp.
Oh and I also have the "High Dynamic Range" box unchecked. I've read a lot of other posts saying to leave it unchecked, I would agree with this.