mech fan blade rpm limit?

A 4000rpm limit does not mean a 4000rpm motor limit. You guys are silly sometimes. If your fan is driven at 1 to 1 then I agree 4k is 4k. But most fans are not driven at a 1 to 1 ratio. Do the math guys.

But all fans should be treated with respect. Plastic or metal. Knocking them about can make an ugly shrapnel mess of things quick.