Tassman,
We still have a few outstanding questions. Top on the list has to do with the nature of morality and the difference between deriving a descriptive claim, such as
Doing Y will bring about X.
and a prescriptive claim, such as
One should do Y.
Or, perhaps more to your point, the difference between predictive descriptive claims like
I will do Y.
and the above prescriptive claim.
You refer to the difference as "merely semantic" but I quite literally do not know what you mean when you say this.
The difference is important, because you concede that science does not derive normative claims (and hence does not derive prescriptive claims), but this is what morality is. Morality is not about what means are sufficient (though, of course, such information is used in deducing what we ought to do) and it is not about predicting what one will do (though, again, this can be useful in deducing what we ought to do). It is about what we should do. If science cannot tell us what we should do, then science cannot draw moral conclusions.
But you have said that, nonetheless, "What science does discover are testable premises upon which rules of behaviour (i.e. moral theories) can be
reasonably inferred." (Bolding mine.) I'm not sure what you mean. Rules of behavior are obviously normative in nature, and science does not derive norms, but (from what you've written) one can make a "reasonable inference" from the descriptive claims of science to the normative claims of a moral theory.