mech fan blade rpm limit?

Another thing to consider is the usage. Fans have a way of stealing minor amounts of horsepower and not always consistently. In the car that I built for the wife's drag/street enjoyment. We will loose just under a tenth when we have to turn the lights on for night racing. A counter to that is - turn the lights on even in the daylight. But a fan can kick in at any point in a run or even not at all. Yes, even clutch fans.
Street only car - the point is mute. Run what you like. Personally I run a dual fan electric on my streeters and a single electric fan on my race. I like the electric's for the space and safety aspects. Hands and fans - nary the two shall meet.