For the sake of curiousity, I also completed POD with this party w/ Champion difficulty. Everyone ended up as level 31 mages (before the final battle). The intial levels were 2 x L14 paladin, 1 x L10 ranger, 2 x L15 ranger and 1 x L12 cleric. POD seemed significantly easier with a setup where every character was able to cast the most important and powerful magic-user spells.
The most curious thing was that when everyone had a Globe of Invulnerability in major battles, many monsters ceased to use their special attacks completely or almost completely (for example, dracoliches and blue minions never used their lightning attack) and beholders couldn't do a thing. In some unfortunate cases, a pet of kalistes managed a disintegrate attack. In the final three battles, most of the characters didn't even get hit. Probably some shortcuts have been taken when implementing some of these features (they are implemented as Level 3 lightning bolts?) and game doesn't use anything except melee attacks. Out of several test runs, in the last final battle the green dragons breathed acid only once or twice (not sure why).