Sabi nga ng iba the additional sustain on the setneck is a myth. I read an article (can't seem to ind it) where a Luthier created 2 same guitars with different neck joints. The sustain and sound was just the same, he even tested the frequency on an oscilloscope.
The debate on on sustain started when the strat was compared againts a Les paul. The Les paul had more sustain. But of course both guitars cannot be compared. For bolt ons, the trick lies in the neck pocket itshould be as tight and as close as possible wood to wood.