Baud rate change slows down void loop and stepper motor speed??

Other Hardware LEDs and Multiplexing
2

Depending on the amount of data and frequency of transmission the serial.print() function will block and wait for the FIFO to have some room.

I suspect that could be a problem at lower bit rates.

In your case the "frequency of transmission" is very fast as you are calling stepper.currentPosition() every loop.

Rob