I'm really uncertain what to look at right now for BiS pieces. Cataclysm builds and MMO-champion/WoWhead and the PTR all list different things for the stat changes coming at 49s. I'm presuming that your head, chest, legs, feet, and ring will be a set piece (IE Postmasters for clothies, I haven't looked deeply into other sets that we're getting). Until I get something really definitive, I'm not going to look way too deep at stuff for all classes. As it stands, almost every clothie piece is going to be swapped out, maybe with the exception of Ban'thok Sash.