You will need a bike with 36V 15AH battery to have the range for windy days.
If you live in a hilly area, a crank drive or a large motor (Ezee/BPM) is better than run of the mill bikes.
Be mindful that second hand commuter bikes are difficult to resell, you would probably save a lot of money buying a cheapo Chinese for the job.
One of my guys took a Kudos Arriba home,16 miles each way-32miles total-the Arriba has a 36v x 10,4 Ah battery,he had 2 bars out of 5 left on the battery capacity display,probably good for another 10 miles. I just don't see the point in carrying 15Ah batteries around,remember you are carrying that extra weight on a 5 mile trip. Unless your commute is 40 miles plus then 10 Ah good battery has enough range.
He rode the bike in a lazy way-letting the bikes power doing a lot of work and the terrain had an average number of hills.
The Arriba has the BPM motor, i think that the BPM,with its torque coming in at a low speed is very power efficient,the energy is not wasted by the motor spending much of its life at speeds below the point at which the power becomes optimum.
The crank drive is in theory the better system,after all it's possible to change the torque reaction of the motor power using the bike's gear system but it is limited by the lack of a good gear system that can cope with the power of the motor plus rider. The Bosch system overcomes this problem by turning the power down in max torque changes.
We overcame the problem on the very powerful Eiger bike by adding the Nuvinci hub but it is an expensive solution.
Whereas the hub drive with the BPM motor seems to simply offer the same performance as crank drive but without the complications or expense. The Kudos Tornado and the new Kudos Typhoon (29er)are the most powerful of any e-bike I have ridden and that includes most of the KTM and all Haibike models,they match the performance of the KTM e-race P and BH Neos ,but at a much lower cost.
I think I have abided by the rules by answering the previous post!
KudosDave