So I went to the tasting room (to put it fancily) at Coors today, an area notorious for being a cell signal black hole, at least for T-Mobile and Sprint.
My Epic had a hard time staying connected to the cell network there, and would flip to roaming/no signal. The GSIII did some of the same thing, but I was able to place a clear call from within the room, send/receive text messages and even update my GMail without too much of an issue, depending on where I was standing.
So, subjectively, I won't say that the phone is a significant improvement RF-wise over the Epic (I didn't have the Epic with me as well to test). But I think it was at least a marginal improvement.
What's funny is that there is a cell site just a couple blocks away from the brewery (810 East Street). My phone is bouncing between that site and one closer to me right now. I guess brewing equipment...and Coors' building...make for excellent 1900MHz blockers.