Oh, I didn't know that there was software to adjust the max amps. I would get a controller that has an adjustable amp range from 30 to 100 or whatever because most lifepo4 can not handle amps over 40 amps so it would nice to program in a max amp of 30. My controller has a max amp of 35 and it works fine and is enough torque for me. My bike goes 28 mph on 36v. It will go about 35 mph at 48v and that's with 35 amp controller. It's a hub motor, though.
Anyway, if you position yourself so that you can only use 40 amps or more, you severly limit the kind of battery that you can get. Most lifepo4 batteries are 2C or under which means if they are 10AH capacity, then the max continuous it can use is 20 amps. So you'd need at least 20AH capacity or more to use it on your bike if you choose 40 amp max draw or you'd have to go with SLA batteries (not a fan of those).
Why would you want to limit the max amp draw? So you won't fry your batteries. So that you can use your scooter/e-bike over and over with those batteries. If you are going to have a max amp draw of anything over 40 amp, you'll need more expensive or bigger capacity batteries (which are more expensive) .
Here is how the batteries break down
lifepo4 = usually 2C ( so max amp draw on a 10AH would be 20amps)
SLA = usually max amps is about 200 so no problem there with those kind of batteries
LIPO = anywhere from 15C to 40C so no problem with these but using them at those kind of high C draws will lower the life of the battery and also cause potential fire
Why not get one of the 1000 watt motors with a 48v controller? LIke this
http://tncscooters.com/product.php?sku=106175
(you can see the LB37 controller is an option with this motor)
with LB37 48v controller ...has 10 - 50 amp max output.
http://www.tncscooters.com/LB37.php
I'm not familiar with building an e-bike like this so I'm suggesting you go with the suggestions on the tnc scooter website. If you want more information on Kelly controllers, endless-shere.com forum knows about them.