Under the hood of Keyboard Maestro question.
Which action is faster to trigger inside a macro?
A) Keystroke action as a trigger
B) Select Menu Item action?
C) or a script?
Or is there any difference?
I've got a macro that's firing off lots of stuff, and I'm trying to find the most efficient timing parameters
Select Menu Item action is the safest as it handles timing / race conditions better than a keystroke.
I cannot comment on acripts as there are others better qualified than me to do so, especially in Texas 
I going to guess that there is no material difference between A and B. No need to even consider C, unless you are already using a script for other reasons.
If you have a modern, reasonably fast Mac, then I doubt you could detect the difference.
However, if it is that important to you, then I'd suggest you run some timing tests, in a real-world environment. Each Mac is different, and it could make a difference on a highly loaded, slow Mac.
If you could be more specific about "firing off lots of stuff", then we could probably be more helpful.
I know this is only a single keystroke but I’ve always found the typing action slow. I’m told this is the fault of Mac OS.
On the other hand I can’t think menu selection to be super optimised for speed.
Underneath, the menu item is directly tied to an Action method, which will execute as soon as the menu item is selected. So I have no reason to think that would be slow.
But I think a shortcut key would have to resolve to a menu item, and then be executed.
Six one -- half a dozen the other. 
... and two threes.
I think we’re agreeing.
