@nightmare90gt To expand on what @dc42 has just said, you set the maximum speed in config.g, presumably because you know what your machine is capable of, so why allow the slicer to override that? What is particularly bad about having such commands in the slicer, is that they will persist until the firmware receives another M203 command. That is to say, if you print something that has an M203 value in the slicer start gcode, and then print a second object without cycling the power or otherwise forcing config.g to be read again, that second object will be limited by the speed set in the slicer for the first object.
