Just tried Thief Gold for the first time I already forget the default res it started up in. I switched it to 1920x1080 and all the textures look fine, but the FOV feels really skewed. Also after I got the sword in the tutorial, while holding it up or blocking my guy's arm is really messed up. It's either stretched too long or crumpled up. I'm assuming the widescreen is showing me things that were originally hidden by being 4:3 but even when I switched it to 800x600 the arm was still messed up and the FOV felt off. I can't find a FOV slider anywhere so I don't know what the real issue is or how to fix it.

tried TFix?

I thought the GOG version already incorporated TFix?

If not, does TFix give us a way to choose FOV?

it does, but it's a lite version, you will have to patch up if you want the full thing. one way or another, FOV needs to be changed manually by editing cam_ext.cfg with a notepad type of software of your choice, no matter what build of the game.