The E30-400's are comparable to 300W wheelchair motors (half a Bosch GPA750). But with the big difference that your avarage heavier wheelchairmotor can be overvolted and survive.
Ampflow motors are "hot wound", meaning that they are already on the limit of the voltage tolerance. Even running those without a load on the specified voltage will heat those up to "less than touchable" levels.

With the right gearratio and some additional cooling mechanismes those can be used for a heavy. But with less than 4 it will be a slow one.