Jesus, I give up on you Bryce
You fail to acknowledge even the most obvious facts
So you have doubts that a 40 class racer is more stiff than a 40ft Oceanis?
The 40 class racer has much more hull form stability, being much beamier with a much flatter hull and the 40class boat has also a much bigger B/D not to mention that it has all ballast in a torpedo at the end of a 3 m draft while the Oceanis has only a 2 m draft and a keel with the weight more distributed.
How the hell do you think stiffness it is obtained in a sailboat?
Stffness is invariably created by hull design.. plain and simple. You can roll your eyes all you want, but it does not change that fact. However, for this discussion, not sure why we care.
Here are the facts. Modern wide bodied racers get their righting moment from wide hulls. They are lightened as much as possible to reduce hull resistance. This provide the best acceleration. Because they are lightened so much, their center of gravity is often higher than a good rough water boat.
The most obvious example of a high CG boat having a large righting moment is a catamaran. Clearly the righting moment is created by hull design, not mass. Wide racers use the exact same idea, only with a single hull.
For a modern racer, the keel mass only needs to be as heavy as required to provide a certain amount of moment to balance the standing rigging and to allow the boat to have a RM diagram that extends to a large heeling angle. The total weight is often defined by rules. So the goal is to reduce the hull weight to an absolute minimum and instead place any left over weight on the keel.
Your suggestion that the Class 40 boat is a good rough water boat undoubtably comes from racers whose goal is to go fast in spite of the weather.
Lets put a 65 year old couple on that POS racer and let them get unexpectedly caught in mid Atlantic like the big blow last year November?? north of Bermuda for 3 days. Since there is only two of them, they will not be able to sail through, so they will be forced to resort to stabilizing tactics. I bet they will have a radically different viewpoint than you on what a rough water boat is. Not everything is about performance.
As far as I am concerned neither of these boats are rough water boats. Picking one over the other is like asking which one will be less miserable in rough water.