for that example the fortitude gives more effective health.
but the difference is very very minmial. it was a difference of less than 20.
i assumed a 300SBV for comparision.
36495.54 with fort
36487.18 with armor
typically though armor is going to give you more effective health once you factor in buffs. however. if your armor exceeds your hp by about 30% the fort pot will yield more effective health. Once you factor in buffs such as fortitude and kings often your health will exceed your armor and the defesive potion is better.
i see no reason ironshield and defense wouldnt stack. one is a potion and one is a elixer. i have used them in conjuction, however, i didnt go in and look at my armor since ironshields only have 2 mins and well... i was busy tanking.