A lot of the world record gold splits have extremely fast mouse movement (cough cough blastbolt). If your sens/dpi is too low would it make it harder or impossible for you to lower your golds to that level?

There are top level runners who use pretty low sensitivity so its not necessarily a limiting factor. However I would say the majority of speedrunners prefer sens in the thousands. If you feel like your sensitivity is limiting what you can do then raise it, otherwise don't worry about it. It is first and foremost personal preference

Thank you a bunch!

There's one particular mouse option that could serve as a limiting factor which happens to be the Pointer Precision option.
In your PC settings, go to the devices and click on mouse settings and under the related settings panel on the right side, click on additional mouse settings and then click on the Pointer Options tab and under 'Motion', uncheck Enhance pointer precision if it is still checked and it most likely will be by default.
Doing this will fix the radius of your mouse's motion so there won't be instances where your mouse will jump into acceleration. This doesn't just apply to Getting Over It but also a lot of FPS games and you'll notice a stable feeling with this option unchecked. So with Enhance pointer precision unchecked and high mouse sense, you may just find the right touch into speedrunning more efficiently. Of course this is still a preference thing so it may or may not apply to you very well.

sorry for dumb question, but is it actually possible to see the in-game mouse sensitivity as a number? I just recently downloaded anjo's modpack. In readme file there's this line:
"- Changing sliders: Plus and Minus (will change the slider with tenths precision)"
It doesn't seem to work for me at all... would be grateful for some clarification

villay if you are using modpack then press ctrl+m while in game and then click glitchless 5 times. This will open debug menu and you can see mouse sensitivity with a number alongside it at the bottom

thanks for info bro, appreciate that