"02-09-15: Csontos
I think it would be useful to get a subjective description of just what the attributes of a 'fast' amp are sonically. What does speed sound like in an amp in comparison to mediocrity? Anyone?"
All components contribute to a systems illusion of speed, so its hard to isolate just the amp. But overall, from a subjective perspective, you need to listen to how the system is reproducing the attack, resonance and decay of whatever instruments are on the recording. When the attack, or leading edge of a note is being highlighted more so than the other 2, you'll probably interpret that as speed, or PRAT.