It's not going to help much at all.

Jetliner speed is limited by the need to stay well clear of Mach 1--a subsonic airframe that busts it might very well go down. Even if you don't actually exceed it you have to be careful of nasty effects if the airflow over any part of the aircraft exceeds it. (And remember that wings are based on making the air flow faster over the top than over the bottom--that's what generates the lift that keeps the plane in the sky.) A U2 at cruising altitude flies so close to the edge that if it turns too fast the inner wing can enter a stall buffet at the same time the outer one enters a mach buffet.