So far, all ships listed don't have a speed higher than 6. Of course certain talents, most notably Full Throttle, allow pilots to push beyond their ship's listed top speed. As it is written, there is nothing stopping someone with this talent from taking an A-Wing or a TIE Interceptor for example to beyond 6, however there are no mechanical rules regarding maneuvers and range bands etc, beyond chases and narrative effects.
So it is possible to go over speed 6? Or is that supposed to be a ceiling>