I have only played BF4 with the 14.1 drivers. But my FPS went up by a LOT. I was playing on a 64 man servers that was on Shanghai. Played for about 5 mins, was averaging mid 40's for frame rates. Sometimes it would just sit at 30.
I then switched to Mantle, relaunched the game and joined the same server, and I was nearly always at 60 with drops to 50ish now and then.
I DID however get the stutter that some others reported. Every few minutes or so I would drop down to single digit frame rates for about 1-2 seconds. Then it would come back up and start running fine again.
This was with the machine in my sig playing at 1080P High.