Whats oddest is i was SA these in just full Empyrean+2 and switching out Accessories only (To try and force a Set bonus) and i was doing 900~1,200 Dmg on SA's... So when i saw a 4,531 needless to say i was a little shocked.
Which leads me to believe the THF Set bonus might go beyond just flat "Triple Damage"... Needs moar investigating =x
4531, nice O_O
I was trying to do the same the other day against Dhalmels in Altepa while farming, without switching out of my 4/5 AF3+2 items (missing gloves +2, was wearing *** Armlets instead for TH), but when Triple damage did proc on Sneak Attack, I didn't get an unexpected result like you : 2977 damage, with normal Sneak Attacks doing about 1000 damage.