Coming at this from a different angle; I believe that you turn slower while in motion not from momentum (or at least not just from momentum), but from drag. The faster your ship is moving, the more drag is applied to your ship. I'm not sure if this is universal (ie: the faster you move forward, the higher angular and vertical drag as well as longitudinal drag), or specific to direction only (longitudinal speed only effecting longitudinal drag, angular speed affecting angular drag, etc).
Experiences leads me to believe there is some kind of universal effect. It feels that the faster your ship is moving, the more difficult it is to go up and down; as well as turning. So slowing down/stopping by throwing the ship into full reverse appears to make the ship turn faster, or rather that moving your ship longitudinally reduces your ability to turn effectively. I could be wrong of course, as I haven't actually tested any of this; it's just how the game 'feels' to function.
