Here's a pic that tells a story.
This was taken when a friend and I did a 3 day mixed surface trip. You can look at the height of the seat compared to bars and resulting postures to see why each bike has a different saddle. He is 25 years younger than me and I can't bend like that no more
He was faster on pavement, we were even on the Coquihalla summit hill because I have far lower gearing, I was faster on the loose gravel. On day two we did 227km's. Different saddles, different bikes with different postures, same ride.
And my bike does not really look "Posh" by any stretch of the imagination.
