I have very little skin in the game here, as I don’t personally have a strong desire for an acronym...but my 2 cents are that “Reasoning carefully” can be shortened to “Reasoning” (or “Reason”) for this purpose with no loss—the “careful” part is implied. And I think I identify more with the idea of using careful reasoning than rationality. “Reason(ing)” also matches an existing short definition of EA as “Using reason and evidence to do the most good” (currently the page title for effectivealtruism.org)
I have very little skin in the game here, as I don’t personally have a strong desire for an acronym...but my 2 cents are that “Reasoning carefully” can be shortened to “Reasoning” (or “Reason”) for this purpose with no loss—the “careful” part is implied. And I think I identify more with the idea of using careful reasoning than rationality. “Reason(ing)” also matches an existing short definition of EA as “Using reason and evidence to do the most good” (currently the page title for effectivealtruism.org)