I'm a 91 Magician with EMVIII Focus.
Pet had the following:
Manaforged Plate
Alteris Heirlooms
Visor of Vabtik
Spectral Armament (Fire/Wind Swords)
Burnout X RK.II
Iceflame Ward RK.II
Velocity
Embercoat RK.II
Arcane Distillect
When hit with Spectral Symbiosis RK.II, the pet was hit for 2,233HP of Non-Melee Damage, and it's hit points decreased from 100% to 96%, so it was a 4% drop.
4% goes into 100% 25 times. 25 multiplied by 2233 equals 55,825. So this pet with EMVIII, the basic magician buffs, and summoned items for a level 91 has ~55,825 hit points. I forgot to buff pet with 2.0 Epic Primal Fusion, so add 1,000 hit points if you have your 2.0 as well.
--EDIT--
Just Leveled to 92 and Equipped My Twitching Snood EMXII Focus.
Pet had the following:
Manaforged Plate
Alteris Heirlooms
Visor of Vabtik
Spectral Armament (Fire/Wind Swords)
Burnout X RK.II
Iceflame Ward RK.II
Velocity
Embercoat RK.II
Arcane Distillect
Primal Fusion
When hit with Spectral Symbiosis RK.II, the pet was hit for 2,233HP of Non-Melee Damage, and it's hit points decreased from 100% to 97%, so it was a 3% drop. 100% divided by 3% was 33.3. 33.3 multiplied by 2,233 equals 74,358. So at 92 with EMXII and the basic pet buffs this pet has ~74,358 hit points. Subtract 1,000 hit points if you don't have your 2.0 Epic Click.
Edited, Feb 22nd 2014 4:22pm by VonsneerTheScoundrel