Over 200 hours in, all dmg increase perks from sneak and archery, including making bows 2x more powerful than base. Full smithing tree.
One shotting an ancient dragon can't be done without looping potions or ench/alch.
Doing the maths... an Ancient Dragon has HP a shade over 3000. Even with triple damage from sneak, plus your poison, you'd have to have a bow doing in the range of 950 damage. Tell me where to find this bow. I want one.
crafted dual enchanted. will post pic. wait one. IIRC I was using this one. sneak 3x, archery maxed, I can't remember the poison, but the dragon didn't resist. I can't recall but I think it was on expert mode(at time of vid). Doesn't look like I critted the dragon either.
Hmmm, can not find poison, that was used..time to scour gamesaves. and trust me, when I screw up, or the game's auto-aim/aim assist kicks in/out, I get my ass whooped just like anyone else.
/edit bow pic
http://i.imgur.com/KBMlf.png