To be honest ours stays mainly on the middle groove and we go from high to low. That's only 'cause we are lazy!! (and that's why I've just bought a gear head drill!)
fast for small drills slow for big ones and use cutting compound there are charts with exact speed but its not that critical . just one offs quarter speed does all
me, I'm lucky...have roughly 8 pillar drill's, plus 2 high speed/drills (10,000 and above....plus 2 mills....
have drill bits of common sizes fitted to the drill machine....need a diff size hole just use a diff machine.....
only then do I alter speeds for special holes and then prob easier to use the mill and a rotor broach cutter......
U CAN never have enough pillar drills.....hahaha.......