given a song with a double bass pattern hitting on every 16th note (or comparable subdivision).
if the snare hits are on the upbeats, either 2 & 4, or the upbeat (the "&") of every count, then the metal being played is power metal.
if the snare hits are on the downbeats, either every count, or every 8th note subdivision (aka blast beat), then the metal being played is death or thrash metal.
Exceptions:
Amon Amarth- Death in Fire. (Melodic) Death Metal, but snare hits are on 2 and 4.
DragonForce's power metal and uses blast beats. (Although take Through the Fire and Flames for example, it's a bunch of spastic trills, arpeggios and chords with little to no melody. It's odd how they're power metal in the first place so this exception could be argued)
By this theory I'd say Wintersun does not fall under the "power/harsh Vox" category, due to the excessive use of blast beats. I guess they'd be Melodic Death, or (iirc wikipedia says, though I don't fully agree) Melodic Black.