If you want to live through any boss fight as a tank, the one thing that you need above all else is health. Stamina, which gives ten health for every one point of stamina, is by far the most important stat that a tank needs in order to do their job well. No matter if you have reached the armor and defense cap, or if you're producing more threat than your DPS can keep up with, you won't live for a lick if you don't have enough health.
Defining minimum health is an important concept in end game raiding and groups. For most instances, a minimum of 10,000 to 11,000 unbuffed is needed. This will at least let you take a few blows from a boss before dying, hopefully enough blows that the healer will be able to get off a few heals on you. For more entry level raiding environments, it's necessary to have unbuffed health between 11,000 and 12,000. If you've got 11,500 hit points going into Kara, you'll probably be able to reach 13,000 health fully raid buffed. This will let you survive a good portion of Kara, which means you can get more gear, which begets more health in the long run.