As for how pickups handle sustain, low output allow more natural sustain (string vibration) and high output (passives) create artificial sustain lengthening the audible string vibration. Actives do both at the same time... in the expense of tone maybe(?).
Can you explain the physics behind your statement please?
Low output pickups produce a weaker magnetic field that doesn't pull the strings as high output ones do so they let them vibrate more freely. However high output pickups have a higher "gain" so with less string vibration can produce a stronger signal and as the string vibration dies out they can still be heard.
Actives have a weak magnetic field which lets the strings vibrate more freely again but they use a preamp to amplify the weak signal of their weak magnetic field. They have high gain via transistors than the coil winding and a stronger magnet like passive high output pickups.
I personally prefer the passive high output pickups tone though. ;)
It seems that whenever transistors get in the way they leave their signature...:P
Edit: Also passive pickups are made only of conductors and magnets. Actives have semi-conductors (transistors) in their circuit too. Their tone has to do with that I guess. It may be something about the very heart of their construction (composition of the transistors - you know germanium, sillicon etc).