Originally Posted by Sixty Fiver
For aggressive riding the B17 would not be my first choice as it is better suited for more upright riding.
I'll quote it because it's the truth, but everyone will read right by it.
Brooks B17s are designed to be ridden with the bars level or higher than the seat.* This, along with the appearance, is why they're popular amongst those randonneuring weirdos. If you have any sort of drop, you'll want to get a Swallow/Swift/etc to be truly comfortable.
All saddle companies make different seats for different riding positions. For a more upright position, you really need a wider saddle to support the sitbones and keep the happy areas happy. For a lower more aggressive position, you need a narrower saddle to give you better thigh clearance and basically stay out of the way. Imagine the pelvic rotation between the two positions. You're basically riding on your sitbones in the upright and riding more on your taint in the down low. There is no end all be all saddle that works with everything, or it would come equipped on every bike.
*Cue the guys coming in saying that their B17's are comfortable with 18 inches of drop on their converted TT bikes.