Dale, thank you for you comment about the spreadsheet. One thing I'll point out, it doesn't (yet) handle profession-changed characters.
To my understanding (current theory), lets say your character is now level 20, having achieved 17 levels as a Mage and 3 as a Bishop;
For spells in the Wizardry spellbook, you can learn any spell up to Level 6
For spells in the Alchemy, Psionics and Divinity spellbooks, you could learn up to level 2.
I did similar to you, but waited until my Mage got to level 18 (so he could learn level 7 spells), then changed to a Bishop. Best thing I did! Sure he didn't learn as many spells as my pure-Bishop, but had more spells than if he'd stayed a pure-Mage.
Visit
http://wiz8.web1000.com/perko.html if you want to learn more on how spell availability is determined.
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