hey I just upgraded to a Sapphire HD7870 from my old Sapphire HD6870 but when I now play BF3 the performance is the same or even worse ;(
with my HD6870 the auto settings were all on high 16 filter AA post on high AA deferred off,
with my HD7870 now its
everything on medium
texture quality on ultra
AA deferred off
anisotropic filter 4
and the fps are jumping from 20fps to 80fps with an average of 35fps or so I guess --> with my 6870 I had 45fps while recording,
to record I use fraps its really important for me to have decent fps while recording since I'm running a yt-channel as hobby
I also noticed that my gpu usage wasnt 100% somewhere around 70% I made a video so you can see it for yourself
my cpu is somewhere around 70% too.
I noticed the same problem in BF3 with my 7870 FPS numbers jumping around, had GPU usage in the 90's didn't play it for about a week get back on now it sits between 60-75 % and 90+ at the load out screen where you pick weapons and spawn back in . In Shogun 2 I get GPU usage in the 90's+ and in Heaven benchmark its pegged at 99% usually. My guess is its after a update they pushed, Dice patches one problem only to have more come up.
limit your max fps to 60 and you should increase your minimum and as a result reduce stutter and fps droop.
im sorry to say the bulldozer cores do seem to have issues with the frostbite 2 engine. so look about and see if you can find a tweak or patch that may help your game run smoother.