If you are truly unsure, order from wallbike.com, they have a six month unconditional guarantee on Brooks and Berthoud.

By the way, I have a B17 and a B72. I love them both. The B72 is on an old Ross mountain bike with a tall quill for an upright position. My B17 is on my LHT. I love them both. The B72 was comfortable immediately. The B17 was immediately comfortable too, but not incredible for all day rides. It too about 800 miles it became incredibly comfortable. I absolutely love the B17 now. Saddle adjustment is extremely important to get right no matter what saddle you get. I found I had my saddle too high which caused perineum pain. I sorted all that out on a trainer over one Winter. Once I lowered the seat to where it belonged, the pain went away.

I did begin a tour with the B17 with only about 150 miles on the seat. My first day was 70 miles and I still felt good.