I've never done that exact combination, mainly due to my dislike of the Thief. I find it is the most worthless use of a slot in the party. I've done 2 Black Belts, Red Mage, White Mage and had success. I've done 3 Black Belts with a Red Mage and had a lot of success. I've done 4 Black Belts and completely raped the game after hitting level 10 or so. It was almost as unfair as 4 Fighters, but a LOT cheaper.