My impression of unloading was that it was due to a reduction in the angle of attack, hence reduction in drag, of the prop blade as forward airspeed increased. Reduced drag, hence increased engine speed. With the decrease in angle of attack also comes a decrease in lift (thrust), unless the prop blade was statically stalled (i.e. operating past the peak of the lift versus aoa curve when the plane is at rest). Hence, higher pitch = higher potential unloading. In general, I epected it to be rougly proportional, ie. increased pitch meant increased unloading even if "fully" unloaded is never acheived. None of which is meant to make any particular point.

When a plane exceeds the pitch speed. Is that what is called "wind up"?

So... for practical purposes (not racing) the take home message seems to be: no special treatment for the needle just because the pitch is on the high side - tune it normally, and see how it behaves in the air.