[JoshTriplett]

This also depends heavily on information density. I can listen to some types of content at 2x without issue; other content I can't accelerate more than 10-20%.

[MaulingMonkey]

Some content I have to scrub and rewatch even at 1x speed.

Some content I can watch at 4x.

[dnautics]

Blind people regularly teach themselves to listen at 4-5x speed.