PvP gear should be considered a full tier lower than PvE gear, especially since it cannot be reforged. Epic PvP gear is about as good as heroic PvE gear, so wearing Epic PvP gear is not that bad when stepping into raids, but you want to start replacing them with raid epics asap.
We had two paladins joining us during WotLK who were Arena freaks. They did ok, but the Retri was complaining how he missed way too often, and the Holy was going OOM in no time. After a week or two-three, they were decked in full PvE epics and their Raid performance went up bigtime.
PvP gear seems to lack on hit and mana regen mostly, having resilience in it's place.