I think you're expecting a bit too much from them.
My H has been a faithful workhorse in the family for 50 years. HOWEVER, it has its limits. It will hit 24 mph in 5th gear with no load, but you need a rolling start in 4th and it takes a long time to get there. I wouldn't even consider pulling any kind of load in 5th.
Even in 4th, you run out of ponies real fast with any kind of a load.