Macbrea said:
You will notice that all the spells listed in the books that can be made permanent on yourself are of 3rd level or lower. Righteous might is a 5th level spell. The question now can a 5th level permanency allow for a permanent 5th level spell to be attached to a person. You will notice that Magic Fang is available as a choice but Greater Magic Fang isn't. Ask yourself why? My guess would be it was done for game balance reasons.
I don't think game balance is a limiting factor, at least not as much as you think. The Permanency spell does a pretty good job of keeping itself balanced by using increasing caster level requirements (spell level + 10) and XP costs. For each spell level of the spell you want to make permanent, there is a 500XP cost associated to it. For example, to make a 1st level spell permanent, you must spend 500XP. To make a 7th level spell permanent, you must spend 3,500XP. Technically, there isn't a limit as far as what you can do, except for DM approval of course.
Here's the kicker though. Sure, if you want to, you can research a permanent application of a 9th level spell for yourself, though it would cost you the standard time and resources to research the spell, you must meet the caster level requirement of 17th level, and you must then spend 4,500XP. But the balancing factor is this. All it takes is one successful dispel magic from another 18th level caster and BOOM!, you're permanent spell is gone. So, all that time, all that money, all that XP just got blown away by a simple Dispel Magic.
Not very pemanent if you ask me, and the very reason that the spell itself has no spell level limitations. What level spell you wanna make permanent isn't a big deal. The spell itself, however, is.