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This is highly likely to overload the PC Serial port (200 messages a second including readings etc), and will also very quickly cause the Plot Chart window to lag behind the data.

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That would help, but without understanding why the 5ms interval is important its hard to expand further.  One option we have demonstrated in the past is to buffer your readings at e.g. 5ms, and then after some interval send them back to the PC with a slower interval (e.g. 50ms) to display on the plot chart.  This is demonstrated in the below video which shows the electrical "bounce" on a switch connected to an Arduino via this approach:

YouTube Video: https://www.youtube.com/watch?v=wwRawju55nk

If you can expand more on what is the aim here we can likely advise further.

Example
If you are testing that the Motor Controller is affecting the speed of the motor quickly/accurately then you could use an opto coupler or reed switch to measure the speed of the motor spindle, which can be averaged and reported every e.g. 100ms via the Plot Chart while testing, and only requires minimal circuitry.