The Spirit Realm

btw, you want to make sure you are using the same level/class npc to do all these tests (ideally the exact same npc.)
also, i would suggest PoR instead of OoW. with newer expanions we always see the AC soft cap going up. we may get a beter idea of what value ac has by using new content instead of old content.

There are still returns over the softcap, they're just smaller. It's still a matter of tradeoffs. Which would you prefer, an improvement in survivability, even a marginal one, or +100 mana? To many of us, survivability impacts playstyle SO MUCH more than mana pool that the AC choice is worth making. AC vs. HP both impact survival, and that's what parsing and statistics are about, feeding those discussions is what threads like this one are for. Mostly, though, AC vs. HP hasn't been a real choice to make since Velious. Everything basically has both. Better gear has more of each.

The improvement you percieve as your AC increases might well just be the corresponding increase in hp (better AC items usually have more hp too). When you look at how your health bar reacts to attacks, you are looking at relative effects - a 1000 dps mob is going to be more noticeable at 8000hp than 12000hp for example.

Also, I seriously doubt you would notice the effects of 2% shielding, the effect is just too small. 2% Shielding reduces the hit by 2% of a minimum hit. You only actually get 2% if every hit is for min, and that never happens. The damage reduction on a max hit is much smaller (more like 0.2-0.5% depending on the values for DB and DI)

2800 AC...sheesh... by comparison, Jaraman foolishly tanked the summoning drachnid spiders outside the Vorganoth mission with barely 2000 AC. With only a gimp PoP cleric to heal him, loaded with DI, there were quite a few quick heals thrown in between interrupted CHs. To hear a high end shammy giving testimony to the differences of 50 AC at 2500+ shammy is encouraging, altho I don't have the spare DKP to do anything about it.