For a competitive advantage, you definitely want to favour higher refresh rate. You will on average see enemies sooner when coming around corners etc, because there's a lower chance of someone appearing right after a refresh.
The short answer to this is: more FPS is better. You will see enemies sooner and experience less of what feels like input lag (lag between you pressing a button or moving your mouse and something happening on your screen). Even if your monitor won't get a new full frame on every single refresh, you will get at least a partial frame that has more recent information. This video explains it nicely: https://www.youtube.com/watch?v=N8ZUqT6Tfiw&t=495s
Here are a couple of other sources to back this, because FPS capping is sometimes a topic of heated debate.
https://www.youtube.com/watch?v=uzp8z1i5-Hc&t=40s
https://www.youtube.com/watch?v=nbHCU--VvpQ&t=542s
As far as I'm aware, legacy (and even 2.60b) support adding visible field to the sides instead of zooming in when using a wider resolution. Additionally on legacy you shouldn't even need to change your cg_fov when doing this. However I'm not sure if this is limited with ultrawide resolutions - maybe someone else knows better.
Edit: Shoutout to Aciz for pretty much all the info in this post, I think I learned all of it from him.
