Some of those ratings are relative to when a string was introduced. When it was released it may have been a 5 at the time but then other more modern strings that were given a 5 now are worlds ahead of the old 5's. also as a rule of thumb a string that is .75mm thick is probably really weak. That's thicker than the bg65 which most on here say doesn't have a lot of repulsion unless you want to string over 30 lbs. with a .75 string maybe you wanna take a panda power to the magic 40lbs to get any power from it.
from what i was told by badminton alley, ashaway measured their thickness before tension was applied onto the string, whereas yonex measure their thickness after tension was applied. please correct me if i'm wrong.
i've used ashaway microlegend xl which was measured at .73mm and boy is it powerful. it is also durable.
anyway, take their ratings with a grain of salt, i, from time to time, would disagree on some of their ratings.