I have both the B17 and the Flyer on different bikes. For a long while I thought the springs in the flyer were so stiff to make them almost redudant.. so I did some reading and fould that they are basically set for larger riders, and meant to take the shock out of holes in the road. As with any brooks you have to persivere and break it in properlly, as you already have the B17, you'll know that well. I have not tried the B66, but I understand that has softer springs.. whould be worth checking the specs for that from Brooks or their agent..

Know that I know the springs in the flyer are stiff and understand whats going on and as its slowly breaking in, I do see a difference over the B17, but it does take time.