As V gets closer to the speed of light, you'll be attempting to get the square root of a smaller and smaller number until you have a time dilation factor of 0. This basically means that time will pass instantly.
So the faster you go, the quicker your journey will be, except that time will pass normally to everyone else, so by the time you arrived at the end of the tradelane it's entirely possible the human race would be extinct.
Also, it's impossible to reach the speed of light, and if you went by our solar system as a guide, it would take many years just to get from planet to planet (with our current technology that is).
My final point? Freelancer obeys pretty much no rules of physics, so stop worrying about it and enjoy the game.