I believe A1-5 scale is only used on Japanese Wagyu. Australian Wagyu go by a M1-12 scale and American Wagyu go by the Prime, Choice, Select scale.

From my personal experience, i've had A5 and M8 wagyu and i would say the marbling on the A5 is on a whole different level then the M8...and i would grade Prime American Wagyu below M8. Unfortunately i have never had the opportunity to try M12 wagyu