The key difference between the Pace 500 and 350 models is speed. Pace 500 is a Class III ebike that can go 28 MPH on pedal assist, while Pace 350 is a Class II ebike that tops out at 20 MPH on pedal assist. Both have a throttle capable of 20 MPH without pedaling. The Pace 500 uses a 48 volt system with 500 watt motor, compared with the 36 volt / 350 watt system on the Pace 350, so the Pace 500 produces more torque and accelerates faster.
Riders who want to go as fast as possible will appreciate the Pace 500 extra power, riders who don’t want to go that fast can save some dollars with the more economical Pace 350.
Some states restrict the use of certain classes of ebikes. For example, Class II ebikes might be allowed in your location, but not Class III ebikes, so check your local laws to decide.