Most hub motors have a hard time climbing steep hills unless they are built like tanks. Big enough to ram more than enough amps through them and they will move up steep hills despite the lack of gears.
In the state of Washington 1000 watts is the legal limit of output for a motor on a bicycle; 1500 watts for a moped. Unfortunately it is harder to get a moped registered than a power assisted bicycle.
1000 watts will drive 400lbs up an 8% grade at about 12-13mph; possibly a little more if pedaling hard, but only if the gears are correct. That is too slow of a gear to drive around in all day if you want good mileage.
The new Xiongda two speed hub motor has a max out put of only 720-740 watts (when run on 48 volts) and will slow down to about 9-10 mph with 400lbs (total combined weight) on an 8% grade; and you may need to pedal hard. I need to test out one of these motors.
If you live in Canada you will probably need an additional gear reduction to the drive wheel at 500 watts, and it will be crawling up the steep hills of Vancouver.
I think the best way to motorize a cargo bike would be to use a Nuvinci infinite gear hub like the Elf car does. But use a two speed gear box to reach the desired gear reduction from the motor. Then directly to the brake side of the Nuvinci with a Gates GT3 belt; thereby using the Nuvinci to help your legs keep up with the motor. But this Xiongda hub motor looks like it has fabulous potential.
Mid-drives are popular, but for a cargo bike with 400-450lbs (total combined weight) they can destroy your drive chain fast, way too fast at 1000 watts! If you’re obsessed with a large motor like the Stoke Monkey you would be better off using it as a mid-mounted motor, driving the rear wheel through a stronger chain or belt. But don’t let me stop you from finding out the hard way; after all if you accelerate slowly and don’t stress the chain out much it may have reasonable life span.
Also be aware that these Chinese two speed hub motors are new and unproven for durability by power obsessed Americans. But keep in mind that the only bicycle power systems that are proven by time are old technology, and have problems that the sellers will never tell you about.
See this review on Endless Sphere forum. The internal gears of the Xiongda may require better grease.
Some e-bikes have torque sensors that make the motor run intermittently, making a jerky motion. The Xiongda
Much more information on this article https://www.electricbike.com/2-speed-e-matic-xiongda/
Bidirectional hub motor with unidirectional two-speed output
US 20120302390 A1
A two-speed bidirectional hub motor includes an electrically driven hub, including an electrical motor, oppositely aligned one-way bearings, and a planetary gear system connected to the electrical motor. A fixed shaft is connected to the stator of the electrical motor. The first of two one-way bearings connects the electrical motor to the planetary gear system, and the second one-way bearing connects the electrical motor to the hub casing. When the rotor is electrically activated to spin in the forwards direction, the second one-way bearing engages the hub casing and rotates the wheel forwards at high speed. When the rotor is electrically activated to spin in the reverse direction, the first one-way bearing engages the planetary gearing system, rotating the wheel forward at lower speed by a gear reduction. This design gives two-speed output without a transmission.