Well, I've finally started on the FF7 Game Mechanics which, when finished, should be a group of four guides which will eventually cover most, if not all, the various formulas used in various parts of FF7. (The Date Mechanics would be an unofficial part of the Game Mechanics, since it's already out and finished at this time)
Magic formulas are actually pretty easy. Base Damage is already (Magic atk + Level), thus all that remains is to work out the modifier. For example, Fire, Ice and Bolt's modifier is 3, while Fire2, Ice2 and Bolt2's modifier is 7.5. (You multiply the modifier to the Base Damage)
However, that's obviously not the whole story because you have to factor in the Magic def of the enemy as well, and other factors come into play; most spells when cast against all enemies will do less damage (2/3 of the original power). Some spells that can only be targeted against all enemies will do more damage if there's only 1 enemy to be targetted. And certain spells ignore those rules and do full damage to all enemies (Summons are notorious for this). There's also formulas for Random Variation, Piercing damage, Elemental rules to follow, special weapon formulas, etc....
I'm not going to go into exact detail here, but I will warn you; the Game Mechanics guides will be quite a while coming. There's still a lot of stuff I need to find out, but most of the hard work is already done. (Finding out the stats on all the enemies is going to be a pain though)
HTH. HAND.