And, unless anyone is super opposed to it, add a prep time AP.
Qawsed found some solid prep time feats that scale to epic characters, highest of which is 7.8 Teratons and requires significant time to st up but once done can be used pretty instantly.
Here's how I believe it should go, for the few pages we have here already.
Tarrasque should scale to Epic Level characters (7-C). His durability should be placed as being, depending on what prep time feats are acceptable (I can repost them here if it makes it easier for cataloguing), somewhere from 6-C to 6-B, as he isn't even scratched by most prep time spells. Keep in mind the Tarrasque is such an obscene threat that even epic adventurers would normally steer clear of it, and only a wish (a prep time spell itself) can make it vulnerable at all (not permanently kill it).
Dragons should maintain keys for lesser and greater dragons. Lesser dragons should scale to higher level but not epic spellcasters capable of using Earthquake (Low 7-C). Higher level dragons should still scale to their own dragon breath.
Empyreans should scale to Earthquake users at Low 7-C.
Krakens should scale to Earthquake users at Low 7-C, with their island wiping over an unknown period of time acting as a supporting feat.
Epic Characters (Mordenkainen, Drizzt, Elminster, and so on) should have Low 7-C to 7-C normal AP and up to the prep time AP with, as said, prep time (so 6-C to 6-B). Their durabilities likely should not scale to that prep time AP, however.
All the godly avatar stuff is an adventure for another day.