Hubmotors are virtually never the most efficient solution, but they more than make up for that by opening the door to ebiking to a wider audience due to the simpler installation. I say they are viable as it's always better to get more people involved in ebiking than not. They are best used in territory that isn't extremely hilly. To get specific weights for various hubmotors, try these sites.
http://www.texaselectricbikes.com/ca...ontr-c-37.html
www.evsolutions.net
www.evdeals.com
Good luck!
Robbie