So what are the real advantages when using FOC (Field Oriented Control)

When using a 16bit timer as a hardware encoder interface, That´s 65536 ticks per revolution. Or if using a 8mm screw -> 8mm / 65536 = 0,000122mm. 

Less then a thou mm precision when direct driving it. 

To reach e.g. 1400mm/min with a direct drive 8mm, we then need 1400mm/min / 8mm = 175 rpm or 18.32 rad/s. 

We could also consider a 2:1 gearing, which will double the speed to 175 x 2 = 350 rpm.

I have started using the CORDIC for the sine/cosine calculations, and it seems fine. Perhaps a bit less vibration. The way S_FOC is using floats does not use the full potential of the CORDIC, unfortunately. It is very precise though.