your fov is smaller/narrower which is why it feels faster in the horizontal and if its 4:3 stretched it makes the enemy gamers look wider(I think shorter? technically). The only downside to 4:3 is that it is slowly being dropped as something natively supported by games.
in certain cases it feels better due to higher fps. Only FPS game i run 4:3 is CSGO due to the low enough dips/frame times and i found just ballparking the sens to what you feel is right was more of a placebo for aiming in there rather than doing sens calc 16:9 1 @ 800dpi -> 4:3 .7xxx depending on how i was feeling that day.
(wider ratios in general) buy you more viewable area but at the expense of lower FPS and more area to "monitor" while playing. I believe most recommend 1440p+ once you start pushing closer/past to 27in monitors.
Just use whichever you feel is better and would be better in the long run for your health. might be worth giving up the extra viewable area to enable you to sit a bit further back/ergonomically, which isn't really something most think about but can fuck you up should you sit for prolonged amounts daily outside of games. As a fucking DUMB example: I'm planning on going from a 24in 144hz benq xl2411 to a 22-23in 144+ w/better tech as I shift from grinding to just wanting to play for fun and want more space and better aesthetics.