You will find things appear to move slower at higher frame rates. This is because your eye has more information to work with. Adding motion blur will help by filling in space between frames so it doesn't appear to jitter rather than rotate but at higher frame rates, the motion blur trail will be shorter, making the motion seem slower.
Using a lower frame rate with motion blur will make it appear faster.
You could render an image of the rotor with motion blur at a low frame rate and add it as a plane parented to the rotor. This will give you the long trail you'd expect, even at high frame rates.
raising the rotation speed with motion blur enabled should also do this but I'm assuming you have already tried this.