Movement rate of special armor - celestial, elven or mithral

[Rycaut]

So I'm looking to upgrade my Cleric's AC from his current AC 20 (+1 chainshirt, +1 heavy shield, ring of protection +1, dex +1) ideally while keeping my movement speed at 30'. I have about 16k gp to spend.

I'm looking at a few options:

Celestial armor (costly but the daily fly and +3 chainmail equals really nice) but I'm unclear what the movement speed would be. Is it the 20' due to chainmail even though it is very light?

Mithral or elven chainmail? Same movement question. Not sure the price savings is worth it.

Are there other options I should consider?

[Stikye]

Mithril is considered one armor category lighter. So Medium mithril armor is considered light for the purposes of movement speed.

[Archaeik]

To answer the rest...
Elven and Celestial are 1 category lighter than normal, not just 'considered lighter'

Speed reduction is based on category, not the base item.