I don't think it's possible to have over advanced timing with any load given the way we tune our glow engines for peak (or a little below) revs. Any hint of over advanced ignition will cause a loss of power and therefore loss of revs which would immediately be thought to be too lean a mixture. Not long ago I put a 13x6 prop on an ST45 just to see how it'd run. It was flat out at 9100 but showed no signs of stress and tuned as easily as usual.