Also I'm talking about a DIY level here with smaller table top machines, not people that converted older CNC or Non-CNC machines over.
OK so we're most likely talking about steppers then because if we're talking servo we wouldn't be concerned with $200 for a SS.
The Smooth Stepper is capable of driving at 400KHz the stepper motor drivers.
The Arduino Due is capable of driving its digital outs at 12MHz ( Ben Hack on Youtube tested the Arduino Mega which is slower than the DUE and was able to hit 8MHz ) which is twenty times faster, however with the TRE and you even run Embedded mode under Linux or Android which would take it to a whole new level of development.
Not sure why you've latched onto the output switching speed as being of any particular importance to your point but as you have let's take a look...
Hmmmmm 12Mhz.... let's do the maths....
10 microsteps - so 2000 step/rev for your stepper motor (if you don't know why I've picked 10 then look it up)
12000000/2000 = 6000 revs/sec
multiply by 60 = 360000 - yes indeedy - that's a stepper doing THREE HUNDRED AND SIXTY THOUSAND rpm
Now that I'd like to see.
Let's take your figure for the SS
400000 / 2000 = 200
multiply by 60 = 12000 rpm
Now that I'd like to see
So let's come at it from the other way
I don't know what sort of definition you get with your repraps but would 100th of a mm be reasonable to discuss?
I pick that because it just happens to be the "theoretical" resolution of my router.
I have my rapids set to 10m/min - not unreasonable I'd have thought.
So at 10 microsteps that's 10000 * 100 = 1000000 steps/min or 16666 steps/sec i.e. ~16KHz. That's WELL within Mach's slowest kernel speed.
So please
- make whatever points you like but let's have less of this nonesense about output switching speed.