We used to prop Nelson .15's on our QM airplanes for about 27,000 RPM on the ground. 18,000 RPM isn't that high...
Current day .40's on Q40 planes run in the mid to high 20's also. In the air, probably around 28,500 RPM.
F3D .40's are likely up in the low 30's. I don't fly F3D, so I can't comment for sure, but they're hauling.
Of course, no one expects them to last forever, either.