Here is my AC which I didn't even really try very hard to get.
10 base
1 dex
14 Armor (Blue Plate)
9 Shield (Madstone)
5 protection item
3 natural (Seal of the Earth or just as easily Bark pot)
2 dodge (chaosgardes)
1 haste (pots or crafted clickie)
45-
2 Recitation (Long lasting self buff that is absolutely not hard to keep going)
47 standard AC
5 human versatility boost
52 AC that is quite achievable using only Madstone shield as raid loot
The vast majority of mobs in this game will need more than a 2 to hit you with that AC (47).
And as for Quicken being the most important feat in my opinion, I can't think of one that is actually more critical. Sure you want Max for your blade barriers, probably empower too. Maybe some Mental Toughness. But when the **&^ hits the fan in raids or other tough fights. You want quicken to make sure that you can single handedly keep the entire party up. When it's looking like trouble and you can hit 2 max'd mass heals within 1 second and everyone is back to full health...well let's just say I consider that powerful. What other feat can allow a cleric to solo and/or be the sole cleric in the Reaver raid for example?
Perhaps less important on the halfling marked builds as I have heard that the marks are not interruptable. Still, my opinion is any cleric who has experienced dropping a max'd/emp'd/quickened blade barrier right in the middle of 20 mobs would consider Quicken a top feat choice.