I think you could do 5 miles one way with any ebike you choose to buy if you are going to work and have some time to recharge there.I do 8 miles and I only have a 8ah nicad battery.It takes about3/4 an hour an amp to recharge with my charger. Have you thought about a place to recharge your battery at work?Will you have to take it off the bike and take it in?
I already had a bicycle I like so I bought the Ezee kit from Ebikes.ca. One of its best feature is it is waterproof . I can testify to this..It is a solid kit. Also the hub motored is geared so you get better torque up hills and there is no drag when you dont use the motor and pedal unassisted. I weigh about 205 and can do 15mph up the hills in my area when I assist the motor with medium effort. I rode unassisted for 3 years before I bought the Ezee and I used to go about 7 mph up those same hills.