We have a Hobie Oasis kayak with an Evolve (Torqeedo) electric motor on the rudder. We hardly ever paddle unless the water is just too shallow for the pedals or motor. We almost always use the pedal drives and motor together. This increases our speed versus pedaling alone, and increases our range versus motor alone.
A typical day for us is between 12 and 25 miles. Depending on how hard we want to work I will set the motor between 100 and 200 watts (WOT is just over 400 watts) to maintain an average speed around 4 mph. Because of the GPS in the motor system, we can see in realtime the effects of wind, current, and pedal effort on our speed and range and adjust as needed. We usually try to reserve 60-65% of the battery for the return leg.
On a downwind run with decent wind we usually use the motor and sail together and just relax and enjoy the ride at 5 mph.
Peter