I'd say increasing sens does help as Puck- states, but you could also try to just get used to aiming for a longer amount of time without feeling too uncomfortable while playing those long maps, I for one sometimes just pause the game at a break or very slow part to readjust the placement of my mouse. Something that also helps is just getting a bigger mousepad, although again, increasing sens helps a lot, take a look at doomsday's liveplays and see how he deals with mousedrift (he has insanely high sensitivity though, so you might want to just increase yours a little and not as much as his sensitivity)
