ArM doesn't use the Roman Pace ... the ArM pace is "about a yard" or equally "about a metre" (if you are modern, but even less paradigmatic than the yard)
It used to be 5 ft, but some reality checks reulted in the Arm5 pace being revised...
Hmm well that's a point on which I, personally, would have to take issue with the writer of that particular conceptualisation. Measurements are what they are, not a matter of being whatever one arbitrarily wishes them to be for his/her own convenience.
A pace (~1.46m) is a concept that would have been commonly understood in the medieval paradigm as it had been employed widely by the Romans in all manner of construction.
Might as well call a foot an inch or a cubit a yard if measurements can just be reinvented as one wishes.
Measurements can just be invented as one wishes 
Although I do agree that the Roman pace seems like an excellent unit to use in ArM.
I'm used to the metric system, so measuring things in paces, pounds, or so on is a mess for me. Regardless, I'm pretty sure ArM5 actually defined "pace" in a round-about way in one of its pages... perhaps the discussion of Aquam Individuals, or the near the size table... sloth parma, but it's there somewhere.
Well, since I have already posted the metric equivalent of the Roman pace you shouldn't have any trouble extrapolating as need be from there. 
For other measurement conversions you can always use these handy online tools that I use...
teaching-english-in-japan.ne ... rsion/feet
Every type of standard to metric conversion you should need is at that site, just use the menu on the left side to get the appropriate converter. 
Given that the game design seems to assume a roughly meter/yard-ish 'pace', and magi can already manage insanely huge spells with that measurement, I'm just going to call that distance a 'hermetic pace' rather than increase it to match the roman pace. My in-game justification will be that, as a unit of distance that shows up a lot in base individuals in hermetic magic, they decided to use it as a unit of measurement, and because of the roman influence on the Order they called it a 'pace', despite the mismatch in actual distance.
As, historically, units of measurement have been far less standardized than they are now and often had regional and cultural variations, I have no issue with giving the Order a sort of cultural variation on the meaning of a 'pace', based on their magic.