Mark, I've just skim read this thread in one turn, so forgive me if I missed the details. Have you got the PSU sorted for the big motor?

I also built a spindle with a large 270KV motor. I then modified a 750watt PC PSU to have a variable output voltage on what was originally the 12V line. Although I can make the PSU output any voltage unloaded, when the motor loads the PSU the voltage drops down the the point at which it can supply that amount of power*. I found that even driving the motor with 750watts didn't give a significant amount of cutting power; I can take 0.5mm cuts with a 6mm tool at 80mm/min but it is not very clean and the spindle RPM is too slow for 3mm cutters.

*The PSU will always limit at 750watts (this is a natural limit, not a protection circuit). Since the load of the motor is fixed (0.36 ohms), and the total power is fixed, the voltage must drop to 16.5V. I decided I need more power, but I'm not sure how to get it; even a budget ATX PSU >1000watts is not cheap.