Unlike the original simulation, the actual motors are not by themselves in free space and I was wondering if the magnetic field outside the motor was going to cause issues. It does. Below are screenshots in steps of 15 degrees for a rotor with a 17mm centre-to-centre distance:

The colours have been capped os that anything over 1000 gauss is purple. I also got torque values and the fluctuation was a very significant: 26.0 +/- 6 mN.m. 

I decided to see what "M-22" laminations would be, as mentioned in the BLDC FEMM tutorial, and the difference is massive:

The flux is completely contained and the torque about the rotor is 29.8 mN.m. At least I know that the ferrite toroids can get 87% the torque of proper laminations but leaks a magnetic field. 

This is in utter contrast to the stainless steel 304 tube idea: