Not just balance. Go ahead and raise all speeds up to 1000000 (max combat speed is 666 I think). Do you know what happens?
It all goes to (a funny and amusing) hell.
Say I drive an Onslaught towards a ship. I happen to hold the w key too long and all a sudden my speed is 200. Now I wait as I fly by my target, barely firing a couple of shots at it.
It gets even worse with burn drive- Engage it once, and you're going 600 su/s. Do you know how hard it is to slow down in a huge ship? :p
Also, talons become op. Any ship with the ability to control these available speeds is essential to combat and can literaly run rings around the ships struggling to catch up/slow down.
And worst of all, the combat barrier. Hit it, and you're going 626 su/s in the opposite direction, facing wherever. In fact, you find yourself trying to keep speed down to control it. If only there was a barrier to stop me from going out of control...
Full circle.