I'm not sure how successfully munchkin it really is, and it's definitely designed for general utility rather than killing things, but I've had the following idea for a Spontaneous spell specialist kicking around in the back of my mind for a while:
- Life Linked Spontaneous Magic
- Mystical Choreography (Can cast ceremonial spontaneous magic at a rate of 5 minutes per magnitude rather than 15, or 1 minute per magnitude if using any kind of prepared space, HoH: S, pg 60)
- Baccaleureus (+90xp to be spent on Latin or Artes Liberales, Art & Academe, pg 90)
- Cautious with Arte Liberales (minus two botch dice on any roll when using AL; can reduce total botch dice to zero)
- Puissant Artes Liberales
- Puissant Philosophae
- Great Stamina x 2
That gives you Artes Liberales and Philosophaie scores of 5 +2 each, with specialisations in ceremonial casting for additional +1s', a Stamina of +5, each Technique at 5 and a few Forms at 5, meaning you're casting ceremonial spontaneous magic as a casting score of +26 (+2 for loud words and gestures) before roll, aura and Life Linked Magic, for any Technique/Form combination. You can therefore reasonably reliably get a level 15 spell in any Te/Fo combination.
The Cautious with Artes Liberales virtue by a strict reading of the rules I think means that you can do this without any botch dice under standard circumstances (although I'd understand an SG who didn't like that interpretation). This means you can add Life Linked Spontaneous Magic to the combination with less risk of accidentally killing yourself. At unconciousness level, that's enough to cast level 35 spells in any Te/Fo combination. Level 50 could be reached if you're willing to take a heavy wound - there's no die to the damage, so no risk of killing yourself. At least, directly.
I'm sure it's possible to optimize it a bit more than I have done. If I were actually to play this character, I'd probably give them some fairly crippling flaws when trying to cast magic without ceremony.