if you start keeping an eye out you will spot the local leafletting firms at work. the ones in my area lock their sack barrows to lamp posts in the area theyre working
i use a fit lad who is very good ,he can do about 500 in 5 hours , but only for 2 days running as its gruelling . i doubt many can keep up that pace long term , from what i see most leafletters are walking at about 3-400 in 5 hours speed.
i would be wary if a leafleting firm tells you their guys and gals walk for 6 or 7 hours each and every day