I know you addressed your question to Rimracker, but hope you don't mind if I attempt to shed some light on your confusion. Like you I'm a Silvercan guy, but had to learn a lot in a short time re B/l motors.

First advancing timing seems to roughly work the same way as in a brushed motor. Advancing the timing gives you more rpm at the expense of more heat. Go too far and you can fry a motor even in a Mini. And yes, you're looking for max rpm and for the most part ignore torque, because of the fixed gearing.

Generally speaking, smaller diameter and lower magnetism rotors have higher rpms. So when you evaluate which "tuning" rotor, you would chose a smaller diameter rotor or a shorter one. Of course this gets complicated cause some makers offer several different strength or magnetism in their rotors.

Apparently, the stator has something to do with performance, but my knowledge doesn't extend into that area.

The other thing that gets confusing is that one manufacturers 0 mark may be different different from another's. Thus, just because you can advance the timing on a Reedy to 50 degrees, doesn't mean you can do that to a Speed Passion. I suspect that if all motors had the same 0 point, there wouldn't be the difference in performance that we're seeing now. I'm sure there would be because of stator designs, but, perhaps not so large.

Tried to describe in simple terms. Hope this was of some value to you.