it's actually the same panel and specs - difference just flat and curve.

really based on your preference but i said go. for flat. curve u need sit right at the center to appreciate, and the difference might not be that noticeable at 55 inch

Since you've gone through the settings and can't seem to find it. Then perhaps it's a feature that comes with the panel and can't be modified. At least not in the usual way. With your fussiness, me thinks you really should have gotten a better TV.. 
Yeah, personal preference.. For me, room styles.. especially in the Living Room? Go for Flat screens. Sure curved might look more pretty on its stand. IMO, curved screens are great when used as in PC monitors style. Cuz you sit right up close and center of the display, pretty much all the time & can take full advantage of its bend.