20% and 5% I think
From a Ultrafire 18350 I got ~20 mins on high (in 4x5min bursts). Theoretically, you should get 5 times that in medium, or 50 times that in low. So 1hr 40 mins in medium or 16.6 Hours in low.
I'd go with round numbers and think of it at 20 mins, 1.5 hours and 15 hours.