I was wondering this too.. i'm a guy with a pretty skinny ass
Back in my teenage years i used to use one of those Bontrager cutaway saddles on my mountain bike (you know, the really really really narrow ones), without a problem.
I just ordered a B17 regular, however, for my Rivendell build. I figured it's probably more comfortable, and if i really hate it, i can probably trade it with someone!
-r