Persistent Spell is balanced by being a +6 adjustment, however the Ultimate Magus can apply it to 5th level or lower spells resulting in mid level casters able to cast 11th level spells. Nice.
What's your favorite spells to Persist? A few of mine.
- Any of the Bite of the X series. Go for several of them to really cheese.
- Improved Blink. Wall? Through it. Hit me? Roll percentile. Visible? Nope! Warning: DMs will throw books at you.
- Nerveskitter. I move first, and I will win.
- Swift Ethereal, if you have Transdimensional Spell. Look ma, no body! More immunities than anything shy of constructs and you still affect foes.