Thanks for the responses.

I know from making my euro paddles the length of the paddle as well as the area of the blades have major influences on the paddling effort and cadence. Add in all of the other variables (blade shape, paddle weight feather, kayak width, paddler height above the water, arm length, paddler strength, paddler stamina) and any rule of thumb is just a starting point for the quest in finding the perfect paddle. The better the first guess the shorter the quest. I appreciate your help.