Why not something like this

I really like the idea behind that and it's similar to what I suggested previously. Why not something like this (ROUGH numbers):
gold wow
PvP Item A has 70 agi/str/int + 30 PvP Power
PvE Item A has 100 agi/str/int
PvP power does not function in PvE "instances", but functions everywhere else.
1 PvP Power = 1 agi/str/int in the open world
1 PvP Power = 2 agi/str/int inside PvP instances

That way both gear types are basically equal in the open world and equally handicapped in the respective instances. I see no reason that PvP gear should be weaker in the open world against mobs. Gear differences are mainly been for instances anyway.