Perhaps explain what you mean by proprietary post...which post?
Will only provide my opinion....most have the opposite problem...they can't push their saddle back far enough.
My opinion is...choosing a saddle because of travel either fore or aft is a poor reason to choose a saddle as
it may preclude the one saddle that is actually comfortable. Generally much easier to change the post.
Perhaps explain which frame and post you use. Pushing saddles forward is typically a better scenario than aft
because the seat clamp ends up under the part of the seat that you sit on.
The Arione has long seat rails but again, I believe its the wrong criteria to choose a saddle.
Good luck.