I can just do 45kmhr with 40t chainring spinning fast, 44t would be better for short periods, 48t for extended periods. 46t on back with 40t chainring and 65nm motor will climb hills where I'm are working to keep front wheel on ground. Not type hill you are likely to find on a road. A 85nm motor would give equivalent of another low gear in climbing ability.
Commuting I'm currently getting 3-3500kms from 11spd chain to 0.75 wear mark, will run the whole drivetrain into ground on 2nd chain so expect at least 4000kms before any issues. Then it will be a whole new drive train, chainring, cassette, idlers and chain.
Because my bike is 32kmhr bike tend to run in 2nd or 3rd gear most of time on flat, both those gears can be replaced individually extending life of cassette.
Commuting I'm currently getting 3-3500kms from 11spd chain to 0.75 wear mark, will run the whole drivetrain into ground on 2nd chain so expect at least 4000kms before any issues. Then it will be a whole new drive train, chainring, cassette, idlers and chain.
Because my bike is 32kmhr bike tend to run in 2nd or 3rd gear most of time on flat, both those gears can be replaced individually extending life of cassette.