You don't get 60% defense from speed, you only get 45% which comes at 24 impulse speed. If you invested in Starship maneuvers skill, you can get another 15%.
Basically it is very useful to keep moving and to be moving as close to 24 impulse as possible because it significantly helps your survival.
everyone should max or nearly max starship maneuvers, its tanking you never have to maintain or repair. and yes you need it to attain the around 60 defense cruiser maximum i mentioned. for escorts it mandatory, evasion is your only defense.