Assuming we ever manage to solve the energy generation problem (and whatever other problems may face it) and build a functioning Alcubierre drive, how "fast" would we be able to travel? That is, from the perspective of an external observer, how much distance could an Alcubierre-driven spacecraft cross in a given amount of time? Or, phrased yet another way, from the perspective of the stellar bodies we're leaving from and arriving at, how quickly can we cross that distance?
Is it simply (not that this is a "simple" matter...) a function of how much energy we can put into it, or does it have its own theoretical limits?
I understand (or at least think I do) that the craft does not exceed c within its local space-time "bubble", but I also understand that the contraction/expansion of the surrounding space-time results in the craft "breaking" that speed limit relative to other bodies around it, and I'm interested in knowing what that speed could be -- hence the multiple phrasings of the question, because I'm not entirely sure what the "correct" way to phrase this question is.