The Wall of Fire (Fire/Fire) and the Four Rules of Tanking

As Hyperstrike's post kind of suggests, if you pursue too much defense with a build, you'll start to neglect other parts of your performance. Sometimes that trade-off is worth it, but not too much. I would be nervous about that build of Hyper's because of the end consumption. You want to be able to keep trucking, and there are many end draining powers in game, making the situation worse if you can't even normally keep up your endurance.

I know people have been able to get their S/L defense on Fiery Aura Tankers to the normal softcap (45%), but that requires some sacrifices... some of which I would debate if they were worth it. I don't think you can get ALL of your defenses to a high amount without considerable sacrifice, just as an FYI.

As to where you are comfortable, 32.5% is all well and good as you suggest (I like it for my Blasters with their ranged or S/L defense), it's not strictly needed for Fiery Aura. You already have pretty high resists, especially if you have Tough, so what does hit is going to be resisted pretty well. The defenses on my main build do make a significant difference, and adding Barrier or one defense inspiration makes it way tougher than anything you face. Unless it's one of those cheating things the developers do with "unresistable damage."

For defenses, I would say S/L or melee, and Psi are the most important things to defend against well. They're the majority of the damage you face or will do a real number on you if you are hit, so you want to dodge those. And getting to the 20s or a little higher with those will make a noticeable difference.

I've been meaning to make a "no concern for cost" build that ups the defense and recharge as far as I can go (making for a good balance there), but haven't had the time. It would require PvP sets, though, which are usually spendy.

You'd be NERVOUS? I'd be crapping my spandex and wishing they sold extra rows of inspies in the Paragon Store!

Agreed.

25% is usually enough to significantly cut down incoming damage.

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LOL to your first part. Running out of end scares me as well! End usage is pretty important for a Fiery Aura Tanker (and Brute and Scrapper, if you're wanting those to be more resilient), because of all the toggles that are worth getting and running. This is made worse when you run into Freaks in the early to mid game, and Malta, Carnies, and Praetorians in the late game. My defensive build is pretty rock solid for end usage, and Cardiac makes the Leadership toggle possible to run. Basically, Consume is there for when a Sapper gets lucky and hits me, or the same for some of the psi users in the end game. I like that a lot... I have a few other characters that need Consume or a similar power to keep on trucking, and that always makes me nervous (even if it is doable).

I'll never scoff at getting into the 30s or even the def cap if I can, but on a resist based set, the 20s really make an appreciable difference. Getting your resists even higher is a big change, too. Cardiac, even before I hit the rare levels and its +1 bonus, made a huge difference in my survivability when my resists to S/L went into the mid-70s, versus the high 60s.