I very much agree with your assessments of the width ranges for the three ski quiver, although I would note that I've chosen to go to the higher end of the listed ranges (with the exception of the powder ski) for skiing in the West & Pacific Northwest. The following quiver has worked extremely well for me:
Firm Snow - Volkl RTM 84 176cm (84mm waist)
Mixed Snow & General Purpose - Ski Logik Ullr's Chariot TT 178cm (101mm waist)
Powder - Rossignol Sickle 186cm (110mm waist)
I have found that this quiver works very nicely and that I spend the majority of my time on the Ullr's Chariot TT 178cm (101mm waist) and have found it to be extremely comfortable in all but the firmest snow conditions. The fact that it has a 101mm waist is tempered by the fact that it is a traditionally cambered ski and as such performs very well in firm, mixed, and moderate powder conditions.
In fact, if I were to put together a two ski quiver, I actually think that I would drop the Volkl RTM 84 (84mm waist) and rely on the Ullr's Chariot TT (101mm waist) for my daily driver out west and rely on the Rossignol Sickle (110mm waist), which has gentle tip to tail rocker, for powder days. I think that the fact that the sickle has continuous tip to tail rocker and isn't cambered underfoot really helps it perform well in the powder despite the fact that it is at the narrow end of the spectrum for a true powder ski by today's standards.