Ok I admittedly was probably the jerk in all this
I don't usually do that, but when I do, I can be a real tool. I think if you notice throughout I admitted that

hehe...
In any case, to BOAT, I envy some of your life experiences and hope to enjoy some of them myself some day.
Here's what we can all know.
The

and the S/D/C's are all great boats.
BOAT, in this entire thread I think you basically were saying that the

doesn't round up vs. boats you have been on. That very well may be true. There could be a few reasons for it... just to think about.
1. As you have pointed out the M & X have dual rudders and are less likely to be angled out of the water vs. a single rudder. Although their effectiveness does diminish with heel and the are capable to losing enough control depending on other factors.
2. (And this is my personal opinion having sailed these boats) another contributing factor is speed & tack (or vector). The mac on heel, or extreme heel, makes a slow boat even more slow. In fact, at heel or extreme heel, the lift and drag produced by the ridiculously undersized boards is reduced futher. If you watched your sail track on a GPS in a heavy blow under heavy heel, you are probably making as much distance over ground to leeward as you are in a forward motion. You are essentially on a run, a slow run albeit, with the boat being blown near the direction of the beam. I'm exaggerating this scenario to make a point.. (If you look at the you-tube videos of both mac's in high winds, they are definitely NOT going fast near hull speed imho).
Rounding up requires forward motion or at least forward force, some vector. The less of it, less drag from the keel and wetted surface to leeward plowing through the water. If the boat is simply laying on its side, being blown to leeward, I don't think it would really round up, at least not as quickly. So if we are going slower, with a smaller keel, and at least one rudder still in the water (which both the X and M have), then we are probably less likely vs. other boats to experience this.
Tangent joke: They all could probably round up a few times, get back under way, and still beat us to the beer station... heyyyyooohhh! I digress.
So, does the mac have a lesser tendency to round up vs. my old P26 which would do it so violently that I thought the thing would break in half? Probably. Its not going as fast, forces are all lighter, and there is far less drag, and the rudders are more engaged ... (probably).
Will it still do it? Most definitely.
Is an M any different than an X with regard to this? Not conversationally and I haven't the measurements to discuss beyond speculation. The hull shape differences and the dagger board (I think is a bit thicker fore to aft?) may contribute to a difference in the computer models but probably not in the real world.
You want to run a test? Dump that ballast and throw some cloth in the air. Sheet tight once you have some speed. The same rules apply to us all. I may do it and make a video of it just for fun.

That would suck though if I went past the point of diminishing stability.
Cheers,
Ed.