Here's what I got so far.
I used the same sequence for the SP as I did in my 290 FPS bench test sequence.
For the MP I played two rounds of 64 man Siege of Shanghai, one round running on DX11 and one round on running on Mantle.
No matter what you do in the MP though you will never be able to get an exact reading because there are to many variables and situations which effect performance.
During the two rounds I played I stuck to the same areas, taking the same routes and tried to keep engagements around the same each time. Luckily, people like to camp around the same areas on Siege of Shanghai so keeping engagements around the same wasn't to hard to do. Also, during both rounds the skyscraper was taken down at the beginning of the round.
One difference between DX11 and Mantle that I noticed straight off the bat is that Mantle is extremely smoother than DX11, both in the MP and SP. This isn't because of any FPS gains either, because the FPS gains aren't big enough where one would be smooth and the other wouldn't.
Considering this is the first iteration of Mantle, and given the fact that it is still in the Beta stages, then it can only improve. When drivers mature, developers find better ways of using it and games are built with it from the ground up not patched in like with BF4, who knows what performance gains we will be seeing. But so far things are looking good.
