i've always been comfortable calling my master Master, and have been called everything from Sweetheart to Toy to 'My whore'
i'm really partial to sweetheart, because it can be reassuring as well as venemous, depending on the occasion and tone
i usually am a 4, since i dont have a committed master right now
when i find one i can truly trust though, i have no problems getting to 7. my only limitation problems would be financial