Hi,
which Cannondale do you have? How much do you weigh? Can you give us an idea of what your riding position is like. The more bent over you are, generally the narrower you want a saddle to be. If you decide to get a Brooks, try and find a place that sells a lot and will take it back if it doesn't work out. The saddles recommended are excellent. I have a Selle Italia Trans AM XLP on my Airborne and I really like the funky little shock absorbers.
I had a B17 in an earlier life, and have been trying unsuccessfully to get another one (Don't ask, I think I am working off some bad karma). If you are a fast roadie, you might look at saddles like the Brooks Pro. There are several skinny saddles that people seem to like, but I can't help much there. With any saddle, give your butt some time to get used to it. Do a couple short rides, especially if it's a Brooks.