Andreas:
I think Mike Palko, Paul Walker and Kim Doherty are all flying the Shulze - I personally do not know who else is using it. Of these three, Mike is the only one I am aware of that has experience with both the Phoenix and the Schulze, so he might be able to give you a direct comparison.
The only comments I remember seeing (from Kim D?) is that the Schulze F2B controller is equipped with a special large heat sink to dissapate the heat caused by our extended part-throttle (and high heat) operations. Castle-Phoenix seems to run cooler naturally, either by design and/or by excellent component selection. Shulze also beat Castle to the market with the ability to simultaneously program the brake and the governor, however Castle has that ability now.
If these folks do not respond here you might try a personal message to any or all of them though the Stunt Hanger PM application.