I just turned down the battle speed and wasted him at more or less the same levels you mentioned in your first post with more or less the same items. The only real caveat I'd say is don't cast any magic on him; he'll retaliate against that in addition to his normal attack, which is too much for Rosa to Cure4 adequately. (I'm told he doesn't react to Bahamut, but I never bothered getting that summon).