What is the difference between 350W vs 500W?
350W provides 60Nm and 500W peak power enough toques and power for your 10% uphill climbing in pedal assist mode for an 80Kg rider. Don’t expect an ebike climbing up hills fast without pedaling.
500W provides 80Nm enough to climb 15% grade for 80kg rider and power up to 750W. You will have more performance using 500W. Select 500W if you need more climbing ability, higher acceleration, and speed; note that more is not always better since it drains the battery more quickly and is slightly heavier.