Soay
Correct - and you might also want to add in the reaction time between seeing the aircraft and doing somehting about it.
It is not hearsay - the FAA have conducted at least two studies to my knowledge.
I can confirm the PCAS units work very well (this maybe what Bose was referring to linking it to a 496) albeit as with any detection system they rely on the other aircraft having a transponder with mode S capability or better.