[AngleWyrm]

What we seem to have going on here is Maximum Speed and Cruising Speed! Allow me to illustrate:

Maximum speed is the maximum number of squares a ship can travel in one turn, based on the Warp Core, Nacelles, Emergency Propulsion, Solar Sails, etc. Fuel storage technologies determine the number of turns over which Maximum speed can be maintained.

Cruising speed is the maximum sustainable rate of travel; how many squares a ship can travel in a thousand turns, divided by a thousand turns. Fuel replenishment technologies are the main ingredient of cruising speed. The Bussard Collectors, Ram Scoops, and Replicators add up to how fast fuel flows into the system, and therefore the maximum sustainable output.

If the Warp Cores were to generate supply units, rather than burn them, it would be possible to scale the cruising speed with Warp Core technology, as well as the operating time at max warp.