IMO you should always gem straight agi, and only get stam when you need to to in order to get socket bonuses. Tanking is only my offspec, but I'm almost completely gemmed\enchanted for agi and I am still sitting at around 34k hps unbuffed, 42% dodge, and close to 50% crit I think. With a few upgrades I'm looking at closing in on 50% dodge in the near future (I can already hit 55%+ with evasion proc and my glyph of indom). Trust me, as a druid you will get plenty of stam from whats already on your gear. It is completely pointless to have like 60k hps raid buffed if you get hit all the time. Its much better to be lower hps but dodge more than you get hit (plus the shielding \ healing from crits and the armor reduce dmg even when you get hit).
See mine? My hps are way lower than yours but I have no problem tanking the first wing of ICC10 at all, and only one in 25 man I dont want to mess with is Marrowgar, but my gear is a bit low for that anyway.
2nd wing on the other hand, druids will need really good gear to handle the hits from Festergut. Rotface is a wimp, but fester can eat a 50k hp tank pretty fast once hes at full power.
Edit: I'm gemmed wrong in a few spots btw, and will be changing those soon. I've been raiding ICC since it opened and consider myself a good player, but I just found out a few days ago that you can put any gem in any slot, its just the socket bonuses wont be applied if its the wrong color...I'm not worried about losing attack power or haste socket bonuses haha.