[MaxWilson]

The manual says it's 10% per point of magic, and I'm 80% sure I've seen it in action. Keep in mind, though, that the fatigue from spellcasting includes encumbrance as well as spell fatigue; you can reduce the spell cost by magic scales, communion, or higher path skill, but you always take the basic encumbrance cost as well. So, 30% less fatigue doesn't automatically translate to 42% more spells.

-Max