This 65" model's specifications show an actual screen/image size of 64.5" diagonal. The screen has a native aspect ratio of 16:9, so the maximum full image width and height are 56.2 inches and 31.6 inches, respectively.
When playing a Cinemascope/2.39:1 film in its original aspect ratio, the image will take up the full width of 56.2 inches, but the height will be reduced to 23.5 inches (diagonal size is about 60.9 inches).
www.screen-size.info has a nice calculator for checking out scenarios like this. There are others out there too, but this one lets you freely input your aspect ratio instead of having to choose from a pre-defined list.