From an Excel sheet I made few time ago, this is the DPS given on main hand by daggers, considering the +205% weapon damage you get from feat + maxed AA:
T4 PvE: 273,69 DPS
T3 PvP: 270,03
T3.5 new: 265,45
Spine: 264,12
House of Crom: 262,06
T4 (other one): 260,04
..
So if you check pure DPS, T4 PvE > T3 PvP.
Difference would be even higher under the effect of situational +Wep Damage buffs (Rune of Grounding etc).
What that list don't show are other stats (crit etc).
Well PvE T4 > PvP T3 if you exclude Constitution (but we are discussing DPS), while spine has similar Crit, but higher CDR and adds Offhand and Fatality and Bel's Mirth effect.
As I said PvE T4 wins on main hand, still spine is not a gimmick to me.