You can but each has more torque than the comparable settings on the 6100. Like I said, if I was carting around massive loads on the regular then I'd probably opt for the 8 but if kiddie carrying is the main use then the 6100 is more than enough, plus there's a pretty big jump in price to the 8.
Thought you can control the amount of assistance?
If I was going to be carrying near (or above) the load limit and had any hills to tackle I’d like to have as much torque available as possible!