Like I said, the 1000c Tuvok stated was probably a calculation based on an average velocity of warp 7 because theres no way Voyager could have sustained a warp 9.975 all the way home...
Unfortunately, there's this other major source for 1000 ly/y: Janeway's "Caretaker" claim is that "even at maximum warp", the journey of 75,000 ly would take 75 years. It sounds as if she is speaking of the hypothetical, physically impossible situation where the ship remains at maximum warp the whole time, and she uses this hyperbole in order to drive home their deep plight.
But it's just as fair to say that Janeway is actually making a semi-realistic projection here: remain at maximum warp as long as physically possible, count in the mandatory pit stops, and you
still get 75 years. In this case, her propagandist point would be that this is still optimism. Most probably, due to assorted adventures and hilarious hijinks, the ship won't be able to maintain this technologically plausible cycle of maximum speed plus pit stops.
In broader terms, I have no problem with the idea that a decades-long journey would always have to be conducted at significantly slower speeds than a days-long one. Indeed, a one-day trip might proceed at a dozen or even a hundred times the average speed of a century-long one, just like a Formula 1 competition let alone a drag race compares to a "ten times around the world" car marathon.
In that sense, equating
Voyager's theoretical maximum speed of 9.975 with this 0.73 ly/hr (or 6,400 ly/y) is perfectly all right. The real problems with onscreen warp factors come at the lower end: the low factors must be fast enough for interstellar travel in reasonable time, as shown many times in TOS and VOY (and less often in TNG and DS9 and ENT).
But those pieces of annoying evidence about "between stars at warp 2" could be circumvented, too. Even if Janeway orders the ship to a target several lightyears away at warp 2 (say, "Scorpion"), and the target is reached within minutes, we are quite free to speculate that Janeway ordered the speed increased to warp 5 after the engines had warmed up a bit, then hiked it up to warp 9.
After all, at the conclusion of many episodes, our heroic captains order a departure from a planetary orbit at warp 1. Surely they must order a higher speed at some later timepoint, when the camera looks the other way. So there may well be a technological reason for starting out at low speeds unless there is a pressing need to do otherwise - say, it's easier on the engines or something.
All in all, and amazingly enough, there are
very few bits of onscreen evidence that would massively contradict the rough speed scales postulated by Okuda and several of the above posters. We don't need high warp to be hundreds of thousands of cee. We don't need medium warp to be tens of thousands. It usually suffices that high warp is thousands, and our heroes operate at high warp despite seemingly initially ordering medium or low warp.
The few blatant instances to the contrary mostly come from TOS, and require very high values of high warp (say, "Bread and Circuses" or "That Which Survives"). The one other instance is ST5:TFF, where a couple of hours at explicit warp seven take our heroes to Sha Ka Ree, reputed to be at the center of the galaxy. But there are several workarounds there, probably worth taking.
The cubic scale as such is unworkable. But something within an order of magnitude of that scale should be perfectly workable in 99.99% of Trek. And the "local variables" theory could well cater for an order of magnitude of variation.
Timo Saloniemi
