Don't forget that on a pure leather saddle the outer margin is over the cantle plate. So the outer margins really aren't for sitting on. (You are sitting on metal there, not on suspended leather)
The cantle plate on my B67 is about an inch wide, tapering down to about 1/2 inch on the forward sweep. So of the approximately 8 inches of territory at the widest part of my saddle, I have to consider the outer 1/2 inch on each side to be wiggle-room, not weightbearing. (the widest part is on that forward sweep) Wiggle room is very important, you want it on any saddle whether it's leather or not.
If you're on the cantle plate (rivets are in the center of the plate, so you can be on the plate but not yet on the rivets) on a B17, please consider a B68 like BSG has.
And Jewell, with 150mm sits you absolutely do NOT want a 152mm B17-N!!! You'd be right on the very edge of the saddle, smack on the cantle plate and have no wiggle room at all. If you really yearn for a B17, try the standard first? (but keep the B68 in mind if you feel you are on the cantle plate of the B17)
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