I find that PvPing while leveling from 75 - 84~ is typically unbearable. Even with heirloom geared players typically having an edge throughout low level BGs it is -nothing- in comparison to people donning Cataclyam gear below 80 or using MoP gear at 80. It destroys any sense of fun in a BG unless you're one of those equipped with such items.
But why did Blizzard put Cataclysm items below 80, or MoP items below 85, and allowing items with an ilevel of 409 to be used at 80? Are they just trying to spit in the face of those who can't afford spending thousands just so they aren't being pounded to the ground constantly? There really is no reason for this aside from trolling a good portion of the playerbase.