I just use the full, 6-man, classic IWD team. Human Paladin, elf Cleric/Ranger, halfling Fighter/Thief, elf Fighter/Wizard, half-elf Bard, elf Wizard. Without any XP-increasing tricks. It's still plenty difficult.

I've only ever solo'd BG2 with a F/T/W. It was... tedious more than anything else, really.