Gemming: Since you are way over the defense cap, don't gem for defense. Also, you are gemming to hit all your socket bonuses the only one that is really a good idea to get is the one in your helm, but use a purple gem dodge/stam or exp/stam for that slot. All other gem slots should be +30 stam. Also put the extra socket from blacksmithing in your gloves and bracers.
Enchants: Once you get into a gear set that can keep you high enough above the defense cap you will want to put +275 health on your chest and armor on your cloak. Your legs need to have frosthide leg armor, it's +55 stam and +22 agi. Once you are comfortable with your level of threat put a heavy borean armor kit on your gloves.
Gear: You need to get that lvl 77 ring replaced right away, you already mentioned the clutch of fortification, so I'm guessing that is your next upgrade. Ick's thumb is not really a good choice for a trinket. The black heart drops in regular ToC5 so it is farmable you can just chain runs until it drops. Another excellent option is the glyph of indomitability it has bonus armor and an avoidance on use(the armor is what makes it good, the avoidance is kinda meh).
As far as what you can tank by your gear, I would say ToC 10 and probably 25 once you get your gems/enchants cleaned up and a couple of crucial upgrades. It does look like you are pretty new to tanking, so I would spend time reading the forums here and work on your skills in heroics. You don't want to get into a pug (or a guild run) and be overwhelmed right away. You'll learn lots of little tricks and what works for you as a tank personally and that will be key to you being sucessful in a raid.
Ye, agree. There's a lot you can do about gems and enchants.
Sort that out then run heroics like hell, and try get into weekly raids and maybe VoA10. If not as tank you can always go as dps, I used to do that to learn the encounters. If you know what you're doing, you don't have to be supergeared to tank a raid.
There's a very good tank axe that drops in Halls of Reflection heroic. Pretty hard fight for a warrior but worth farming for. You can always practise in normal runs farming the shield.
Toronto, Ontario. (I understand I play an EU server.)
I always thought Corroded Skeleton Key was the no-brainer tanking item to buy. Pretty much 2.3k free health and a 6k dmg bubble whenever you need it, could you really ask for more? It's what I did on my protadin, it turned out to be the best frost emblem investment I ever made.
The Corroded Skeleton Key should not be your first frost badge purchase. While it does have a large amount of stam and a pretty worthless on use, there are much large frost badge item upgrades for you.
For example if you purchase the Verdigris Chain Belt you will gain 837 armor and +129 stam if you socket three +30 stam gems. The Gauntlets of the Kracken will give 1257 armor and 118 stam if you put you BS socket in them and gem three +30 stam gems. Both of those cost the same number of badges at the Skeleton Key and you will only gain 102 stam over the black heart without diving into which proc/use is better.
A good thing to do is just grab a pen and paper and compare the stats you have now to the gear you want to buy and judge the benifit vs. the cost of badges. With just a little work you can make a list for yourself where you have already figured out how to proritize your frost (and triumph) badges. I also like to look at the loot tables for the bosses I will be downing and compare that to my list. If there is a drop item that is badge equivalent I had on my list, I might move it below some other items if I know we will be killing that boss soon or it's already on farm.