rotorfan asked:
What I don't understand is how some ships can have such high max airspeeds without getting RBS. Are their rotors turning so fast that the tips are barely subsonic, or what?
The real factors are tip speed and rotor blade total area. The faster the blades, the more lift at high speed, and the wider the blades, the less angle of attack needed for the retreating blade to do its job. So high speed is gained by having more, wider and faster blades. The number of blades is not terribly important, it is the total blade area as compared to the total disk area that counts.
The problem is that more, faster, wider blades actually reduces hover performance, and the rotor system also weighs more with all that heavy blade area spinning around. For these reasons, high speed is a tradeoff against better hover payload.