Maximum output speed is greater than 10M steps/sec without multipliers of any kind.
The programming interface will be very simple. Just upload axis coordinates at least with 250Hz sampling rate and hardware will handle the rest. The simplest possible CNC software would take only few lines of code with gcodecompiler which outputs suitable coordinate data (http://www.oemtech.com/gcodecompiler/).
Mach plugin would be good to have indeed.