For AC, I've found it best to compare epic-CR monsters to the most similar creatures (even those not of the Epic Level Handbook).
In this case, I think the solar is an apt comparison, as are the lower-CR celestial paragons:
Solar: 35 (-1 size, +5 Dex, +21 natural)
Manath: 42 (+9 Dex, +6 natural, +9 deflection, +9 insight)
Barachiel: 42 (-1 size, +12 Dex, +7 natural, +9 deflection, +5 insight)
Kharash: 41 (-1 size, +11 Dex, +5 natural, +7 deflection, +9 insight)
Note that the paragons have deflection equal to Cha and insight equal to Wis. We've already got a Wis bonus here, but I could see adding the Cha-based deflection too.