Just wanted to post a massive thank you for this suggestion about the user.cfg file.
I was at my wit's end with this stuttering issue. I'd tried absolutely everything else and nothing worked. I was about to give up on the game.
Even though you mentioned it didn't work for you, I decided to give it a shot as a last resort.
It has completely fixed the problem for me.
The difference is night and day. I've now played for hours with no stuttering at all, even on High settings with my ultrawide monitor. The game is finally smooth and playable.
So, seriously, thank you again for posting this. You saved the day. Cheers!