I have some info on an S saddle. A friend of mine who rode the Paris Brest Paris this year had a brooks normal sized saddle (sorry; don't know what model) on the back of their tandem. whenever she stood up, the nose of the saddle was poking her. She got the "S" model instead 1 month before the big ride (1200 kilometers). She had many problems* due to the length of time she had to stay in the saddle. But saddle sores was not one of them.

*numbness in hands and feet that did not go away YET, lost toenails, PTSD*