I would highly recommend getting the largest one you can (fit/afford) first. If you're looking at the largest you can fit, then it depends on a few factors. Most of all, will the display be at the appropriate height? I know it's an OLED, but you still want your eye level to land about 1/3 up from the bottom of the screen.
I've seen a GX on a wall and it looks very nice, but ultimately got a CX. Having a CX on a tilting mount gives me a slightly better viewing angle, and gets the screen closer to me by an inch or two. This was especially important as I knew I'd have the top of the center channel a few inches higher than is ideal.
From 10'+ and when displaying something on the screen, you don't even notice it's off the wall.
Decent image where you can see how it is mounted: