With that kind of power I would not think you would need such a wide gear spread. My bike does 30mph in 8th gear at 90 cadence and up hills at 10mph at 90 cadence and it has an 8spd 11t-32t rear cassette. A 10% incline makes me pedal moderately to do 8mph but my battery is not giving me the full 750w of power (max of my motor) and we currently weigh 215lbs + bike. I would think yours would do fine. 11-40 gearing with a front sprocket sized to give you 30mph at 100 cadence in 1st gear would give you roughly 8mph in 1st gear at 100 cadence. the 10-50 combo with 30mph in high gear would be 6mph in 1st. I guess it depends on how much weight you are pushing.
you have to be careful with that motor and internal geared hubs, it puts out a lot of power. i am sure some of the veterans will chime in, I've only been riding for a couple of weeks