I always use the preset party but I change the statistics around.
1. Human fighter, pole weapons , alchemy
2. Slith fighter, pole weapons
3. Nephil thief, edge weapons, lockpick, traps
4. Human mage/priest, initially ineffective but at end of game can cast all spells, edge weapons
5. Human mage , edge weapons
6. Human priest, bashing weapon
My basic strategy has always been once major haste and bless party are attained, then use them! I have everyone attack. My magic users don't hit well, but they do some damage and have lots of tries from the hasting.