Or is the above WW1 bit of trivia a myth? I can understand drilled troops with high quality rifles having a somewhat higher ROF, but I have doubts about the enemy genuinely thinking it was machine gun fire.
To further expand on this, whether the MG thing was genuine or not, were British marksmanship and drills that noticeably better?
Were they able to consistently provide a tangibly greater and more useful volume of fire as a result?
Or is it something a select few were capable of doing in "laboratory" conditions, but had no practical effect on combat?
This answer I've given should answer this part of your question:
To further expand on this, whether the MG thing was genuine or not, were British marksmanship and drills that noticeably better?
As to the rest:
I can understand drilled troops with high quality rifles having a somewhat higher ROF, but I have doubts about the enemy genuinely thinking it was machine gun fire.
And
Were they able to consistently provide a tangibly greater and more useful volume of fire as a result?
Or is it something a select few were capable of doing in "laboratory" conditions, but had no practical effect on combat?
It is unlikely that the Germans mistook British rifle fire for machine gun fire; this was a myth that probably sprung up after the fact. That said, the Regulars were able to keep up a fairly high rate of fire, even if not the 'Mad Minute', considering the conditions of combat and non doubt worries of ammunition shortages from prolonged firing.