Theoretically all objects in space have a maximum velocity of C or the speed of light. Also any object in space, since in pure empty vacaum there is no outside influences, are supposed to remain in motion unless acted upon by an outside force. However, that does not mean all objects move at the same speed, as the only thing that moves at the speed of light is light particle and various other sybatomic particles. Here is the given. All objects must be provided thrust to reach a given speed. If space was truly empty eg. devoid of objects, than constant thrust would ineviatbly lead to the speed of light.
Actually, accelerating to the speed of light is a mathematical impossibility. As velocity increases, so does mass, and reaching light speed would require infinite energy and result in infinite mass.
That why in science fiction you here sometimes when a ship decelerates from light speed the order to fire breaking thrusters is given.
Decelerating from light speed is even less possible than reaching it in the first place. You'd still have to somehow slow an object with infinite mass, plus you'd have to deal with the fact that no time passes for the object in question.
Larger vessels are effected differently because they have more mass, and thus are effected differently by gravity. Therefore they require larger engines, and it take longer for them to turn due to inertia. (an object at rest remains in rest unless acted upon by an outside force. eg. gravity)
Gravity is utterly irrelevant. More massive objects require more energy to accelerate, in perfeclty empty space or elsewhere. End of story.
As these are small they sometimes take more time to move a larger vessel, which has a much larger center of gravity than a starfighter.
Centers of gravity are
a) Points, and cannot be "larger",
b) Not necessarily related to gravity, despite the name, and
c) Not even remotely pertinent
That is all.