i got my achievement today too
i usually jump this instance, or do 3 bosses and waste a couple of try on last boss if i have time.
today done with 5 ruby drakes, at 4th attempt: now im Northrend dungeon hero
5 ruby drakes look for me easier: use 2 buttons, no macros, no rebinding keys, just spam button 1 and 2, and absolutly avoid button 3. but in successful attempt lost 2 of my paladins/drakes.