Stamina is basically free if you plan for it (enchanting, potions, or restoration perks), therefore melee damage might as well be counted double.
My observation and testing would seem to indicate that Archery has no power attack damage multiplier equivalent, and it's just considered a normal "swing".
I'm not complaining, it's just a observation I've made playing two different characters. The Archery character cleans up easier mobs no issue, but my two hander can crunch tougher mobs (albeit at a somewhat higher risk) with a lot less trouble. I think the difference is in power attacks (and the stagger). These observations are for Master difficulty btw.

