You can't do it quantitatively, obviously, and nobody claimed that you could.
What you can do is compare them qualitatively and subjectively, which you'll notice is pretty much the whole thread. There are reproduceable tests that can be performed, they just don't give you a number output.
Not to a great extent. It's difficult to do, but it can be done. It's pretty difficult to roll a car on tarmac in real life too without the help of bumps or other things.
There was a huge fuss way back when the original A-class failed it's elk test, simply because any remotely modern car isn't supposed to be able to do that no matter how badly you mistreat it.
Having never tried to seriously roll a car in real life (and having no intention of starting now), I still think it would be a lot harder than most people expect. It's not the movies, cars are designed pretty much with the specific goal of keeping all four wheels on the ground as much as possible, and that includes making sure the loaded wheel lets go before the CoG has enough force on it to start to topple.