I pull 5 - 16 JD 3100 plows with my JD 4230 100 hp and one with my JD 4040 at 87 hp (I own two identical plows) in grey luvisolic soil in approx 6 to 10 inches of topsoil. We joke locally that we have 6 inches of concrete with hair on it.
I can run anywhere from A3 - A4 to B1 - B2 depending on circumstance. I agree with spray down with glyphosate and it can be plowed either later in the fall or in the spring. When I plowed in the spring I was amazed at how soft and mild the sod had become and the plows just rolled along like happy campers.
The rule of thumb for hp per bottom told to me around this neck of the woods is 20hp per bottom but, as others have said, that will vary from location to location. I was told the target was "traces of clay" when plowing but that is very likely local advice and obviously not practical if you have deep topsoil.
Comparing my comments with some of the other comments supports the theory that specs are highly localized and you should seek some local advice beyond the generalized comments you are getting here.
That's my st..st..st..story and I sticking to it!
Regards,
Dave.