instead of looking at iLVLs, you should consider the following

Melee Accuracy: 480+
Caster Accuracy: 430+
HP requirement: 4k+ on non-tank classes to soak fireballs (if you are 3 stacking, otherwise it can be lower with 4 stacking)
DPS output: Able to burst down non-fireballed conflags, 4 conflags before 2nd necklace break, able to clear snakes before twintania comes back down, does not require caster LB3 to kill snakes, 4 dreadknight rotations before 3rd necklace break.
Tanks: 6k+ HP is reasonable as long as you have proper mitigation skills for each death sentence, combined with timely stoneskins/adloquims

The rest is up to player's individual skill at dodging stuff and team coordination. If you can get all these down then you have a good shot at clearing T5.