I think that I started playing with 0.0 and, very gradually, repeatedly altered my sensitivity by increments of +1.0 or +0.5. I'm of the belief that there's nothing that theoretically is prevented by high sensitivities, whereas anything lower than maximum has an upper bound to turning speed, which can be crucial in close combat. Because of my slow alterations, I never noticed any aiming problems with higher sensitivities, perhaps particularly because I exclusively use buckets. I'm presently at +4.5 and will nudge that up to +5.0 sooner or later.