In my army: 25 gold dragons, 250 high elves, and 5 silver pegasi, plus a wagon, and I had to defeat 4000 diamond golems; the hero was level 17 - Mephala (or Mephalah - translations vary), about 16 skill points (I don't remember exactly), a decent amount of mana (slow spell was also available), and +1 morale; I won on the 20th try!
But how? - I don't understand myself; then I tried to repeat it - unsuccessfully :(
P.S. could you post something like this example with a save file? Or just a large-scale battle ;).