Sorry to step in here, Cary, but wouldn't special relativity still keep such a vessel from exceeding the speed of light? From what I remember working with Lorentz equations, you're still going to hit infinite mass at c. I know you propose that the local speed of light changes, but I'm having trouble chewing on that.
You're quite right... but I'm not suggesting ever "going past the speed of light." Just altering it, locally.
There are two things that this subspace field would do. And, interestingly enough, both are already established IN-CANON as being effects of this sort of subspace field.
First off... per Rick and Mike's work on the Technical manual, the 1701-D's computer cores have "statics subspace fields" which allow the optically-based computer operations to run at FTL speeds. (Which, as far as I'm concerned, is far superior to "bio-neural" computers which, ultimately, are relying on far slower chemical-transmitters which can't really be sped up).
Second... it was done several times, both with DS9 (in the pilot) and with a big asteroid (in TNG) being the ones that come to mind most immediately... a subspace field will reduce the "projected mass" of the object inside of it.
So, you're talking about some value of "c" inside of this bubble that is much higher than it is in real space-time (as observed from outside... ie, from real space-time). It's not 75 times... probably more like 100 or 150 times, maybe even more. The "75c" value I chose as the speed limit using this system is, in fact, where time-dilation effects start to come into significant play even with this system - and that's why I consider this "the time barrier" (as it was described by Jose Tyler).
And you're talking about a dramatically lower "projected mass effect" which means that, when viewed from "real space/time" you might have a mass-shadow of <1% of the ship's real mass. So... if that effective mass-shadow is only 1%, you'd be able to achieve accelerations of 100x what you'd achieve with the same energy output if operating in real space/time rather than in a "subspace bubble."
The short form... it makes you much lighter and increases the speed limit.
It does make sense that such an effect might reduce apparent mass and thereby give small vehicles with little room for fuel tanks enormous acceleration and range, but I still can't help but think that when they hit the speed of light as measured by an outside observer, they're at tau times .001 (or whatever) original mass. Which would still be infinite.
But that's because you're thinking that they're still existing inside of "real space/time." The point is that this little "bubble of subspace" is outside of the "real" universe... it's almost like a little pocket-universe, with transparent walls so you can see in and out, but not limited to the same set of rules.
Or rather, the rules are skewed. Inside of the bubble, you'd essentially see the outside universe as having an effective value of "c" which was far LESS than the "real" speed of light you were dealing with (but you'd be moving at the "real" speed of light as you saw it from your own frame-of-reference), and everything in the "real" universe would be dramatically more dense than it really is. You'd be going at a normal speed, well below the speed of light, and well below the level where relativistic concerns come up. But all the planets, stars, etc, would seem to be much smaller, much closer together, and much more dense.
Drop out of the bubble, and return to "real space/time," and the universe looks normal to you again.
See what I'm doing? I'm not violating those rules you're mentioning... I'm suggesting a way of "side-stepping" them entirely.
With the trip to Delta Vega, maybe the trip did take many months (or possibly even a few years) to an outside observer, but to the crew it was only a few days.
Entirely possible... if you assume that the galactic barrier was just a few light-months or even just a few light-years away from Delta Vega (a "permanent installation") yet nobody'd ever even glanced sideways at the barrier before.
It seems far more likely that they spent a few weeks, or a few months for that matter, at a relatively low but still FTL speed getting back to that first "safe port."
(Granted, the line in the episode says "a few light days" but it's about one light-day just to cross the solar system... so I tend to disregard that line. Perhaps he meant "a few light days under the FTL impulse system" which might well translate to a couple of light-years in "real space")
It also says nothing about how the Romulans could have fought an interstellar war with only impulse ships... or about what the "breakthrough" was that Jose Tyler mentioned, or how "impulse only" shuttlecraft were able to do things that couldn't be done without FTL (things like flying a commissioner from an inhabited planetary system to a rendezvous, or chasing after a starship leaving a system at warp, or investigating a new quasar!)
Either the Romulans had "warp drive" and the shuttlecraft had "warp drive" or they were, in fact, as described - impulse only - but were still FTL.
It all depends on your contention that the local speed of light goes up with this FTL impulse drive. Normally, I'd suggest that you prove that, but since we're dealing with science fiction, I'll be happy to break the rules of logic and instead try to refute your contention ... after I get a good day's sleep.
Well, since the idea that all frames-of-reference are inherently only relevant to those viewing the universe within that frame of reference is at the center of our understanding of this particular branch of "modern physics"... it's not a hard sell.
