About the harmonic feedback & sustain thing ... Slash has got one of the best sustain & feedback harmonics , and he uses 11's gauge... I'm not sure anyway which should sustain more scientificaly , heavy or light gauge.

I think the difference in sustain between different string gauges (or even different guitar models) is realy minor, or more dependant on the pickups & the amount of gain coming out from your amp ... For example, my guitar is a Floyd Rose, Bolt-On neck type guitar ... And it sustains exactly (very little less or more) as any other tun-o-matic neck-thru guitar.

From the Tone point of view , everybody agrees that higher gauge gives bigger tone which most people like more ... But it's a matter of personal taste for sure .