To my bare eye it's the same.
I've retested the same scene from post http://forum.beyond3d.com/showpost.php?p=1820941&postcount=866
With Mantle on:
2980MHz = 57-61FPS (gain of 24FPS on average compared to DX11)
4190MHz = 60-68FPS (gain of 15FPS on average compared to DX11)
This guy reports seeing lower IQ with Mantle on
http://battlelog.battlefield.com/bf4/forum/threadview/2979150493821981180/
might be a bug or a troll, but I think it is worth looking at just to be sure Mantle isn't detrimental to the IQ