Hi,
the UC300 will be fine. The truth is that beyond 100kHz you need to be pretty damn good with your signaling electronics and cables otherwise the signals just don't arrive at the
servo drives.
I have an 1.8kW Allen Bradley AC servo and drive I bought second hand I bought to make a high torque low speed spindle for my mini-mill. I can signal it at 200kHz single ended, ie just a normal
hook-up, or up to 500kHz with differential signaling using the sort of electronics that computers signal each other. To run it at maximum speed , 3500rpm at maximum resolution, 8000 count per rev, requires a
pulse rate of 466kHz. Its doable but I use electronic gearing to knock that back to 93 kHz (divide by 5) and make the signaling situation that much easier.
The only real advantage of the ESS being able to go at 4MHz is if you wish to read a high resolution encoder at high speed.
I might point out that this Allen Bradley servo is the first AC servo I've ever had a chance to experiment with and they make DC servos look like absolute s*********t. They are just so much more controllable
and flexible, I'm not going to bore you with the details but when you get your hands on one you will ask yourself 'why didn't I get into these years ago?'.
Craig