Another reason you can bust 250kts below FL100 is:-
If ATC give you a radar heading or a direct to, followed by "No ATC speed restriction." You aint on a SID anymore so you have no speed limit.
With regard to the 330kts at 4000ft on the Virgin B747-400:- Not sure you would need a 747 pilot to tell us what the bird strike speed limit is. On the B757 is is a maximum of 313kts below 8000ft. This then becomes OUR max speed until we climb above 8000ft.
Eff Oh.
