You are exactly correct about the fact that model numbers do not indicate length except relative to other Montana model numbers--and that not precisely.
Since you mention the 2955, let me respond by saying that this particular model suits us better than any other, but that is to say that your choice depends entirely upon your life style, intended use, and preference. I prefer to tow and park the smaller model and it has plenty of room for us. We are not, and never will be, full timers. We like to take trips, many of short duration, on the spur of the moment. We have storage that suits this size RV. Also towing with a 2500 Duramax/Allison leaves me plenty of "rating" to spare.
We are right now on a trip to Colorado, enjoying the changing aspen leaves and will enjoy the elk "bugeling" at Estes Park in a few days.
http://dwilliamson.com/Aspens/Page.html
Would I recommend the 2255??? Yes, for someone whose tastes, preference, and use are exactly like mine. That is to say nothing negative about the choices that are appropriate for others.
David and Shirley -- East Texas
2955 RL Montana
Chevrolet Duramax 2500 Allison Trans
http://www.dwilliamson.com/mont.jpg