If light travels at its rate unobstructed through a vacuum and has no mass, then this should be the max possible velocity achieved by a warp engine. I think I have kind of figured out that warp drive initiates a warp field creating a spatial pocket to which the ship travels unobstructed like a wave-length in normal space. the pocket is sometimes a sub-space terminology which exists relative to the ship in a solar shell like affect to which all encompassed in the pocket or bubble interact relatively to the fields constraints. In other words light emitted inside the pocket travels at light speed as it would outside the pocket, and objects inside the pocket travel at rates allowable to field constraints. This should be noted that the ship engines propel the ship at up to light speed and the field moves with them.... my thought is that if there is any hope that above light speed is achieved is that the pocket or bubble hits some sort of spatial current launching the ship bubble above light speed and what the engines can do.
the thought occurs to me.... if a spatial stream could be ship generated and it did offer improvement through space as a natural one was supposed to, then arcing that artificially may offer the warp velocities but that's kind of it really... how much can you arc the field emission to generate a spatial stream affect that propels the ship beyond light speed. That's kind of about it. I see faster than light travel as possibly graduating like to this: pre-light speed contained plasma propulsion spatial shell or relative sub-space area bubble light speed light speed vessel encounters natural stream natural stream is artificially utilized warp drive/ faster than light travel
PLEASE NOTE - I did a copy and paste of my own post in the Phoenix at warp thread as it seems to fit here - Starships use a controlled folding of the spacetime fabric in order to achieve speeds not reachable under normal conditions. If you listen to the systems checklist in TMP and TWOK you hear "space matrix restoration coils " and "flux chillers" mentioned. This implies that he greater the energy produced by the warp drive, specifically the warp coils , the steeper the fold of spacetime and the faster the ship can move. It also implies that the warp drive returns spacetime to its original state once the ship had passed thru that particular section of the fold. I suspect that ion and warp trails are caused by this restoration not being perfect but leaving a wake along the path of travel. Modern quantum physics allows for many dimensions that we cant sense but do interact with. The Dimension that allows for a stable fold is called subspace and acts like a brace for the warp to rest on. This is also the dimension that allows for subspace radio to function by sending a coherent signal thru this section of spacetime.
Don't think you can compare velocity of light to warp drive... in warping space-time, the vessel does not actually move, in modern theory... it's space-time around the vessel that does. So a single particle travelling in the vacuum of space at light speed is far different than altering the fabric of the universe and essentially "skipping over the big bunched up folded rug in the middle to reach the other side in one step instead of 5".