I recently e-mailed Buhler asking what the performance differences are between the 3-blade and a 4-blade. Here is the response I received:
"The only difference between the 3 blade fan and 4 blade fan is the 4 blade fan seems to throw the snow better if it is a wet heavy snow. We have tried both fan types at our location, and we really can not tell the difference, but our conditions might be different then in your location.
We sell most of the 4 blade fan snowblowers in Eastern Canada where the snow is wet and heavy."