Sensitivity?

so im stuck with what do with my sens (pc). I've swapped between many sensitivities ranging from 12-12 30 400dpi (holo only btw cause 4:3 84) to things like 12-12 42 800 dpi and many between. all the ones i've tried i do well on so its more a case of what are the positives and negatives of playing slow vs fast sens and not that i cant find a sens that i play well on.