99,999
Absolutely

Here is a spoiler
Because the storyline is 100 percent complete I can honestly tell you that you will not be able to learn Solar Flare the first time you play the game.  Do you remember the picture of the pyramid looking dungeon entrance.  Well this according to my map, which is complete (and I will make fullsized world maps so you can see the entire Continent), this entrance is in back of Palace Apollos.  There is a secret path that leads to this special temple.  Anyway, you can only enter the temple after proving yourself, which mean beating the game once (So say yes to New Game Plus).  There is a Boss in this temple, a sungod no less, who has the ability to do Solar Flare at 999 MP cost.  Upon surviving this damage, and beating Apollos, you earn him as a card, and likewise, the ability to do Solar Flare.  My game engine doesn't allow damage over 99,999 (in a single blow)  to be done by anyone exept...  alas there is a character with the ability to do over one million damage, and effectively is unstopable being that this opponet has 600,000 hp.  But, such an enimy can be beaten in under three compete moves with the right combo of cards.  Defeating such incredible foes is not mandatory so its incredible difficulty should not take away from the game experience (Then again, I have devised one of the cripplingly difficult final battles of all time).