There's always a group of people who do better with insanely high sensitivities but they are only 10% of the total playerbase or so and it's easy to go overboard.
The rule of thumb is that you should be able to turn around 200 degrees without lifting the mouse. To try what sens is good for you, try to hit imaginary targets to the front, side and back but normally, the lower the sensibility, the better precision.
I'm one of those players with a huge sens, I can turn around two or three times to each side before running out of mousepad. I have always played like this and I always use incredibly high speeds when playing musical games so it feels natural to me. I might lower it a bit, tough.
A tip: The smallest movement of the mouse should be far smaller than the size of an enemy from far away so you can actually kill them.
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