Coaches do vibrate n shake at higher speed. there is a tolerance limit when the coach is designed.
Of course, after 110, a coach has to fall, as per some people, but it doesn't.
The coaches are designed to handle high speeds, but IR has its own rules.
SF/Exp, do charge at the given speed.
Over...
more... speeding is a big debate, so there is no use to speak again.
Over all, the crew doesn't over speed at all, exceptional when board orders it directly via HQ.