I have ridden my mare in one for the last 8 years. It fits her well. I like the seat, the twist, and the comfortable ride. I actually bought a second one (in a wider tree) to fit a warmblood I owned, but sold the horse.
I recently bought a used Deluxe Maestoso. I tried a Schleese and a County. The Schleese was very comfortable and squishy. But fits very different than a Stubben from my experience. The Stubben I bought is not squishy, it doesn't have the Biomex seat. But the fit for my TB that is about the same as your description with a large wither is exactly spot on. I do appreciate the close feeling I get with the Stubben too. The quality is great. I bought the 32cm and it's a hair too wide for my girl but her shoulders are so huge the next one down was too tight. Wouldn't trade it. The price was also excellent.
Thanks for all the feedback. It does worry me a bit I am seeing so many listed barely used. I found one with the flap modified for a shorter rider which is great as I am 5'2. Might be a workable possibility.
Thanks and happy riding!
Jessie and The Stinky Pony