Black Assassin:
What i mean is that Pit Fiends are SUPPOSED to be the hardest.
They are Tann'ari (sp?) commanders!
That's why it's a 9th level Mage spell and 7th level Cleric spell.
Balors aren't that tough.
They don't have a lot of spells where as a Pit Fiend has good resistance and lots of Hold and Fear spells.
The Pit Fiend I summoned took on the entire Rakshassa Party guarding the Temple in Suldnessalar!...err okay I did help with Incendiary cloud and Horrid Wilting

But remember the demons all vary tremendously in the game. Max Exp doesn't equal most diificult, quest experience also come in a lot!