Presumably there are no Wish (+ loops) happening.
I don't know what sort of solid T.O. stacking limits there ought to be,
but I'm thinking in terms of the spirit of E6 + smidge of t.o.
If 3rd level spells is a hard cap, this game is rather mute.
With r.a.i. PHB2 Rebuilding in play, I get these in a hurry :
x1 / UrPriest 5s
Duergar Ardent 6s in 2 disciplines only
Beholder Mage 6s (there's a racial emulation trick)
Arty 4s , and Psi Arty 4s
That's quite enough to do something .
My big gun for ability acquisition is the Reason Stealer.
Eat a thing, get it's goodies for 24 hours, Revivify it, to do it again.