As the title says.  It's an extra $110 dollars to get the 80lb thrust over the 70lb Thrust, both for a 24volt system.  why is it so much more expensive? As well as how much extra speed/power/battery life will the 80lb give you over the 70? Thanks 

My dad's Z-7 came stock with the Minn Kota Maxxum 70lb.  He recently upgraded to an 80lb Fortrex and it is a night and day difference. Your batteries will last longer because you won't have to run on the higher speeds all the time.  You also get the extra power when you need to blast through some thick grass.  

The words of Al Linder.  You can never have enough trolling motor. 

 Over the life of a trolling motor, $110 isn't a huge expense.  Given the option, I'd get the bigger one.

bigger is better in this case.longer battery life, motor won't have to work as hard.extra thrust will come in handy.always better to have and not need it than need it and not have it..........