This is something I have thought about as well. I cannot recall, but how do ships move about withing a star system? Do they warp from planet to planet, or travel at impulse?
They don't generally warp into
a system (Jadzia was shocked when Kira ordered her to warp the Defiant toward the Bajoran sun to catch the Bashir changeling in time). Sometimes, if they have a clear path, they warp out
of a system though.
If your traveling at full impulse your going the same speed whether you are a shutle craft or a galaxy class ship. Full impulse is 1/4 the speed of light.
If your traveling 55 miles per hour its the same if your on a motorcycle, a car, or even a large truck. it may take longer to reach the speed, but the actuall speed is the same regardless.
If it makes any sense, "full impulse" is "press the impulse accelerator (gas pedal) to the floor". Unless you have a top speed of 55mph, you're going to keep accelerating past that until you start to level off. And where you level off is dependent on mass, fuel reserves and engine power.