RE: Pletty Advance mystery
Dana, assuming the motor is fine (although I haven't tested by swapping out with a new motor), the prop change seems to have partially solved the problem by putting more load on the batteries.
And the battery-as-culprit proponents also seem to be correct, BUT not because the batteries are fried but because they are 'lazy' from not being pushed enough.
Sorry for the mushy answer. Much preferred to have a Voila! moment with a clear answer leaping out.
I am sure Dave is correct about motors with regard to current state of the art. However after watching Jesky and Shulman flying direct-drive set-ups at the Nats, the gulf between them isn't all that big, or so it seems to me.