Proptop,
I agree with you, the gyro effect of a heacier prop does help stabilize the plane, although the amount is probably not enough to justify the losses. As with everything, it's a trad off, you loose some throttle response with a heavier prop. One thing you didn't mention was number of blades, also a contributing factor. A four blade prop would be more stable in a hover also, but again, you have to give to get. With a 3 or four bladed prop you have to use smaller diameter meaning less prop wash over control surfaces.

I think the gains and losses are negligible with any of the above. The biggest issue is getting the correct diameter and pitch to get maximum performance from the motor (with good pull out and throttle response).

So what we really need is a really long four bladed prop that's extremely light and heavy at the same time, variable pitch so you can flatten the pitch in a hover and keep the RPMs very high to take full advantage of the gyro/flywheel effect, and liquid cooled supersharged engine

Kev