8-9K health buffed is what is recommended for Black Temple, NOT for Tier 5 content. I raided with around 7.5K health buffed all way up to Archimonde with no problems at all. And in BT, on HWL Naj'entus, where his Tidal Wave hits for 8.5k dmg I used Frost Ward to make up the difference until I could get more stam gear. Which reminds me.
DPS wise Spellfire are the best you have until
[Robes of Rhonin] off of Archimonde or
[Robes of the Tempest] or
[Vestments of the Sea-Witch] from Lady Vasj. But if you really feel the need for more stamina, you can drop the Spellfire robes in favor of
[Scarlet Sin'dorei Robes] from Kael'thas in Heroic MgT or
[Shroud of the Lore`nial]. The last robes will let you drop more spell hit gems letting you do the gloves I mentioned in parenthesis;
[Studious Wraps]. You could then gem the gloves with double damage gems and you could afford to drop the hit gem from your shoulders as well.