You shouldn't bother with Break MP Limit as both the major magic users (Yuna, Lulu) both have 1 MP Cost on their final weapons, and you're not very likely to use over 999 spells before you visit a save sphere. I suggest you have a combination of Break HP Limit (even though I chose not to have it), Ribbon, Auto-Haste, Auto-Protect, Auto-Shell, Auto-Regen.