Moving mouse at a "normal" pace, character turns 10 degrees then stops pretty much completely. When using headturn i have no negative mouse acceleration.

On negative acceleration being a means to simulate dexterity, it would be more "realistic" in my opinion to give flat increase/decrease in sensetivity based on equipment (eg. sensitivity * x) or atleast adjust the limits of the negative acceleration.

Complete or close to complete stops are just terrible.