Another great piece of patch 2.3 PVP gear news:

As of patch 2.3 all items in the gladiator season 1, 2, and 3 sets will be part of the same set, so you can use those items interchangably and keep the set bonuses (ie: you can wear the season 2 shoulders along with the season 3 helm, chest, legs) and retain the 4 piece set bonus.