Ok, now it's time to break the rule.
To never ever gear away from survival.
Why would we ever gear away from survival?
Because it's damn fun.
OK, so it's fun. Even tanks like to watch big yellow numbers from time to time. Even a raiding tank could find pleasure with it. There are, however, a few rules we ought to keep.
Your fun shouldn't:
1) Make the run unfun for the others.
2) Disabling you from properly tanking the content.
3) Disabling an eventual co-tank from properly tanking the content.
So it all boils down to being distinctly overgeared for the content. How much is overgeared? I'd say it depends on you and your group. I have fun in the old Cata five man heroics during pugs. I also have fun in an average ilevel 355 set designed to kill stuff. That's grossly overgeared.
Some have fun in content at their own gearlevel, or at least not very much below their own gearlevel. Like having fun in 359 gear with the earlier bosses in Cata raids. I doubt they're pugging it.
That said, how do your start having fun?
Kick your hit-rating to whatever means never missing your target. I hiked it to 8% because I consider the BH 10-man raid to be distinctly easier than some of the old Cata hc:s, and hence I tank it as one. If you'd never consider tanking anything but five-mans in a threat set, then you only have to get hit rating enough to fight level 87 targets.
Kick your expertise to 16. That makes you soft-capped with glyphed SoT. Then kick it as high as you can without feeling squishy, but never higher than 46, because then you hard-cap expertise with glyphed SoT.
Rather obviously, glyph SoT.
Take the best weapon you don't need for surviving stuff that actually tries to kill you and enchant it with Landslide.
Take a very, very greedy look at the PvP gloves, especially if the Conquest Point version is available to you. +5% damage to the attack you'll use almost 50% on boss-fights is an appealing reason.
Glyph SotR and HotR if you feel like having really fun.
Go kill stuff and match DD dps.
There are ways of having even more fun, as can be seen from the link in this post, but this is The Pugadin blog, and pugging tanks don't get to have fun in proper raids, at least not until 4.2 is released.
Now to some stuff to keep having fun without getting kicked.
You'll take a lot more damage than you're used to. The difference between my MDR raiding set and my threat set is a hulking 19% CTC. That's a LOT more physical damage incoming. That's the main reason I don't have fun in the troll heroics. I'd give my healer a heart attack.
While things running away from you basically becomes a non-issue, that extra damage warrants the use of your stun just after you pull a big pack of mobs, and you do want to mark skull. The combined result of DD focusing on your target, your own higher dps and six seconds of target inactivity makes life a whole lot easier for your healer. In effect that target will die very shortly after it's allowed to attack you. Use glyphed Holy Wrath early on stunnable targets for the very same reason.
The above tactics will actually lower your dps a little bit as you take less than maximal damage, but I strongly advice you to follow them until you feel confident that you'll survive the extra damage anyway.
In difference from what I have done, which should work as a reminder to myself to get my act together, don't nerf mastery to increase hit and expertise. Now I didn't go and actively nerf my mastery, but I have been lazy.
When a piece of gear comes with avoidance and hit/expertise I simply don't reforge away from threat into mastery. That's stupid. Mastery is better than avoidance for survival, point by point. What I should do is to reforge, for example, hit rating into mastery and then reforge, for example, parry into expertise. That way I get the same amount of fun, but I effectively convert avoidance into mastery, which is a net gain in survival.
For the very same reason I should probably see if it is at all possible to keep one of my Tol Barad mastery trinkets, preferably the one with strength on-use, and convert 321 points of avoidance into hit/expertise instead of blindly slapping in a hit-rating trinket. This would also allow me to get rid of the inferior 'fun-trinket' with agility.
Then, of course, as gear become more and more grossly better than the content we want to eradicate, we can give survivability less and less of a thought. Eventually we'll tank the content in pure dps-gear, but honestly, I doubt it'll be as fun.