Tick-Tock, Tick-Tock, Tick-Tock...
No responses yet. Finding someone who has ridden both a Rolls and B17 might be a tall order.
One difference is that the Selle San Marco Roll saddle has a nylon shell covered by leather. I can't see that as being very comfortable. The Brooks B-17, like most Brooks, has a suspended hammock style leather cover. The leather gives somewhat and lets you float in the leather cocoon.
I don't know what kind of riding you do, but if comfort in the saddle is important, I suggest you consider some of the Brooks models with springs. Man, THAT is a comfortable ride. I have seriously thought about making an office chair out of a Brooks springer saddle.
For distance riding, one of the important things is that the saddle allows you to slide nicely on it. Some of the synthetics create too much friction between the butt and the saddle.
Besides that, it is a delicate balance between support and give. I think a suspended leather saddle is as good as it gets.
Brooks (England) are good as well as
Lepper (Holland) .