They have the same frame, but the components on the 7.3 are nicer (obviously). It's not just the drivetrain that's different, the 7.3 has a different fork, wheels, seatpost, etc. I have a 7.2, and it's a nice bike. It would work absolutely fine for a 5 mile commute, but it might be worth getting the 7.3. You'll probably be happier with the purchase. Remember though, you'll probably need some cash for commuting accesories too.