de5_Roy :
how mucch does the cpu usage show?
what is the psu model?
off the top of my head, it looks like you might have cpu bottleneck...
if it happens only with bf3, update drivers, get necessary game patches, check power profiles of your pc etc. you could also try oc your cpu higher, try to get more load on the gfx cards etc.
That CPU is more than enough and 550W PSU can handle those cards as well (so even a clunker 800W should have no problems). I am almost 100% certain that 1GB VRAM isn't enough to handle BF3 at max settings @ 1920x1080.
What I would do:
1. Make sure you have the newest CCC (12.4 came out a week ago).
2. Try it again.
3. Turn off Anti Aliasing.
4. Try it again.
5. Set the texture level to the next step down from the highest setting.
6. Try it again.
If you're still having issues after that, try the forums again.
Also, those cards can get a nice overclock with MSI Afterburner, but the memory speed is going to give you a much better FPS increase than a core overclock. I run my 6850's @ 850/1150 and they stay under 70C with auto fan settings.