You guys are all lightweights. I run (mostly in the winter) so I have a nice GPS running watch. I've worn it a few times while mowing; our Thursday/Friday route is all in the same subdivision. On those days I get 10-15 miles.
Once a few years ago due to rain coming I had to mow 39 lawns (all walked with a 48" Turf Tracer) in one 12 1/2 hour day. Had one guy on the trimmer and blower. That day I was over 20 miles when the battery on the watch gave out.
The question is.... what kind of terrain are we talking on those properties? Granted a mile is a mile.... BUT a mile going up and down and across and around slopes, hills, ditches, whatever is a totally different mile than taking a stroll on a flat lawn.