Hi again,
I'll start by quoting myself:
Before seeing your message I tried changing the RollOver ISR to type ASM but it didn't make much difference. Up to 20kHz it works fine, above that it starts to fall apart and I can't really see why.
Correction/clarification somewhere between 17.5-18kHz something happens which makes the TMR2 LP interrupt frequency start to drop. I guess the HP priority interrupts are stealing so much time that the TMR2 interrupts "runs over itself".

At 32kHz the high priority DoStep ISR still tracks the step pulses correctly but now the TMR2 ISR is only run at ~550Hz instead of 1220Hz which can be both heard and felt from the motor. Going higher than this (I tried 33kHz) completely unstabilizes the servo-loop so I don't know how high the INT2 interrupt will actually track the pulses.

/Henrik.