Having slept on this puzzling issue for a couple of hours I was keen to carry out more tests this morning and these are my findings…
1) After regenerating the tool-path (just to be sure) the result was identical to the previous test sample.
2) From another ‘comparative test’ the results from a ‘multi-line’ generated Mcode were identical to the results from an ‘in-line’ generated Mcode – there appears to be no measurable difference in the Mcode execution speed.
3) The ‘gaps’ and ‘tails’ (see previous photo) are not what they seem (and certainly not what I had first thought, in fact quite the opposite) - the ‘gaps’ have been caused by the laser turning ‘off’ too early and the ‘tails’ have been caused by the laser turning ‘on’ too early.
4) Although my Gcode consists basically of…
Axis movement
Mcode
Axis movement
the Mcode has been executed some 10mS ahead of the first axis movement being completed.
5) I take back what I said about Mcodes never being fast enough for laser use and ‘humble pie’ comes to mind.

This situation may change with later revisions of Mach4 and Darwin but currently these Mcodes are too darn quick.

Tweakie.