I think it should be limited to 450.
But it should be limited per role, not per character.
If someone wants to gear up and play both his healers, his tanks, his ranged, his melee and his casters, it should be possible to do so.
(This doesn't resolve the issue of melee having 3 different sets, which is still kinda weird to me...or the fact that one of the melees uses DEX...)