If PBI can cause heat stress to people just standing outside a burning house and is very very hot, wouldnt it be worse in 400celsius house fire heat???
The PBI Gold is designed to protect you from radiant heat, just as much as ambient heat (convection). Hence, inside a house fire, you'll last longer, because the heat takes longer to reach you through all the gear.
The moisture barrier also protects you from being burnt by steam (probably the most common cause of fire-fighter burns).
Ask anyone whose done the Compartment fire behavior course with PBI Gold whether they would want to do it with nomex. I know even though it was stinking hot to wear, when I was in those crates, i was incredibly grateful for it!