Seal of Righteousness in Wotlk is gonna be 5% of AP + 10% of SP times attack speed
lets say u have 2000 AP 600 SP (Sheath of Light) and 3.5 attack speed
2000x0.05 = 100
600x0.1 = 60
160x1.15 (3 Stack Vengeance) = 184
184x3.5 = 644 damage per swing and this is WITHOUT the holy talent improvement (740 with it)
SoB = weap dmg x .35
lets say ur hitting 900-1000 with 3 vengeance, thats 362-402 per swing
so obviously SoR easily beats SoB and the Seals of the Pure talent would be good for PVE