Yep, this is a topic that tends to crop up from time to time. In fact Sean and Jason are both right, thrust is thrust no matter what, But, the difference between 2 engines of similar Static thrust is the rate at which that thrust decays with speed and increased drag. This is because the stuff squirting out the back has 2 components..mass and velocity.

So of our 2 engines the one with the greater exhaust speed will continue to produce useful thrust at higher speeds and ultimately give us a higher top end.

It would be nice if manufacturers quoted dynamic thrust figures also so that we could better match engines to airframe types.

Rob.