While you are waiting on a real answer, I will share my interpretation of this as this was a question I asked Sheldon just yesterday.
As you say a good bit heavier a bass, my understanding is 12 lbs or so. The more mass will effect the sound, most probably more sustain and possibly slightly thicker, meatier. For instance, with the Darkglass pre I think the sound could be compared to other heavier basses like some of the Spectors.
While I like the idea of them practically speaking these are not for old guys like me. The lighter basses are much more attractive. I have an old Kramer that I haven't used in about 15 years because it is just too heavy to be comfortable in a night of playing. But for folks who don't mind the weight, these are an attractive alternative to the lighter Afterburners.
I would think, again with the Darkglass pre, that a person should be able to compensate with the lighter bass to come close in all but raw sustain. And with the Glockenklang I would suspect that the sustain would be slightly increased as well, but perhaps not so much on the " thicker, meatier". Pure conjecture, I do not have one.
And perhaps Sheldon will give you a real answer and explain the toggles as well, instead of my conjecture BASSed on personal experience with other basses. It is really great to have so many options.