The human body is a strange thing in that it senses vibrations or oscillations at some rates more than others. If you move items to the extreme ends of a boat; usually the frequency gets lower; not higher because the moment of inertia is higher. Think about it. If you stand on one foot with your arms at your side it's difficult; with your arms extended easier; with a 12' pole and practice you can walk a high wire. It's due to increased moment of inertia. If you move mass out to the ends on a boat the boat might "hobby horse" at a slower and more noticible speed; not that it was not bobbing before, just that you notice it more now. In an extreme case; a boat that carried the majority of its weight at the ends, pitch stability would be maximized.
I know it sounds counter to what we consider the cause of hobby horsing; but the basic principle of moment of inertia and pitch stability should apply here. Of course; a motorcycle pitch dynamic may still yet to be fully solved/understood so it's also quite possible that a boat hull is a non-linear engineering problem also...
I don't think 50-60 lbs should make much difference on a 12k pound boat; but it -may- induce a harmonic mode in either the boat (or the sailor
) Sounds like a job for the Mythbusters!