Hello OP! Let me put my touring-style 5 cents as well.
General idea is still same and posted previously: butts, legs, arms and spines are different, however devil resides in detail, as always.
@SMSW provided very sharp observation:
The seat does not lean you forward, the distance from your torso to the handlebars does this. A sloped seat will make you feel like you are sliding forward or back, but the lean is you grabbing the handlebars. Before you go custom seat get your riding posture set - a helibar or other brand handlebar spacer will push the bars up and back. Different brands and generations (of helibar spacers) will move the bars more or less than others. Once you get the seating position, and your back right, then go for a custom seat.
ST1300 OEM setup, as I see it with mine 180 cm height and 34" insteam, implies slight forward lean. With handlebar raiser your torso going to up-right position and that saddle slope became awful spine oppressor. This is exactly my experience with OEM and Corbin front seat.
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What I'm trying to say here?
This year I put 0 miles on my ST1300, because it under reconstruction after road crash.
I've rode BMW R1200RT ('Camhead', to be precise, since there are 3 generations) using OEM saddle and found myself spine very happy. My position in it is strictly up-right.
Which diff I noted to Pan:
- No saddle slope caused spine is no longer hurts
- Narrower saddle caused better blood flow in hips
- Knees gets tired lesser (reason is unclear)
How to use it?
Pay attention to your hips, upper (whatever saddle) position may seem helpful for knees, but oppress hips.
Avoid sloppy pilot saddle if handlebar risers instaled.
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Myself personally going to revert back from Corbin to OEM. Then sculpt OEM both pilot and pillion to meet conditions I described, add heaters and roll.
Safe travels!