http://eu.battle.net/wow/en/blog/20131410
"We ultimately arrived at a solution where we set player stats automatically in PvP and increase those stats based on your average item level. Players would understand that their stats didn’t come from gear, but that the quality of their gear does matter. Currently, we’ve tuned the system such that for every point above item level 800, your stats are increased by 0.1%. This means that someone with item level 900 gear is only 10% stronger than someone with item level 800 gear. For comparison, that’s roughly the same increase that a mere 10 item level increase gives in Warlords of Draenor. This allows us to make getting gear feel good in general, while shrinking the power gap to an acceptable range."
Obviously this seems like an example for 110's, but still.