Would a 757 type aircraft be able to fly 400-500 knots at VERY low altitude (20 feet)??
Only over a surface already at high altitude...
Tthough I don't know the Vmo of the 757, the 747-400 (which is a very speedy airliner) has a 365 KIAS Vmo. You would have to be at an altitude where TAS would be over 400 Kt at Vmo (e.g., 5,000-7,000' for the 744).