I've actualyl attained ** with all but 2 characters on the PSX remake version. I actually started doing Pink Nu runs... which is i run through the game, face Pink Nu, get the tabs, then start another New Game +, rinse, lather, repeat. Why? My goal was to get ALL of my character's magic, strength, and speed to ** as well. I actually got pretty far, but haven't touched that particular save file in about 2-3 years. Someday I'll finish it. If I'm not mistaking, everyone's str and speed is maxed out, but the magic is going to take a long while.
Oh, as for the conveyor belt runs, I usually just put a berserker on whatever party members happen to be active, run in there, leave, come back 5 minutes later, then go back to the beginning. Works damn well.