Can i change the sensitivity ingame below 125?

[McSic]

Dpi doesn't change anything beside the speed of the cursor. Look at the polling rate of your mouse instead, that matters for your situation.

Something interesting that many people don't know: Higher DPI can improve the latency and improves the accuracy (means high dpi + low sens ingame is more accurate and faster than low dpi + high sens ingame), see these videos: https://www.youtube.com/watch?v=6AoRfv9W110 (latency) and https://www.youtube.com/watch?v=QrF_e5vKqPk (accuracy)