I've found that with my warlock who has full prideful, that I do much more damage than if I were to PvP in some form of PvE gear, but also take into account old set-bonuses that could be really good for your class. None of the warlock tiers are any good so I just use full prideful and my legendary cloak / Hellscream BoA. Some set bonuses for other classes are really good and can improve damage output tremendously, so it really depends on the class. Also you can use any of the PvP sets for PvP-Power (only Mists of Pandaria sets).