Sean, I agree totally with you. I run with a vfd for that purpose. When I had an Oneida 15" curved blower, I was told to stay within 3-5 hz over 60 and while I got a little more cfm, it wasn't worth the additional noise. I don't remember the actual increase but it wasn't much. I've had better results with my radial when adjusting speed but it is much more loud and the impeller itself is much heavier. What I don't know is how much the housing design and the distance from the blades to the housing affect performance at higher pressure. Dave