5870 Crossfire problem (cpu bottleneck?)

Driver FIY: Latest beta drivers from AMD with clean install. ULPS disabled in the registry.

Crossfire is enabled and both Heaven 2.5 and 3DMark report great scores with 100% GPU usage for both cards in MSI Afterburner. CPU usage is low in those benchmarks.

In BF3 on High settings my CPU usage is between 95% and 98% and my GPU usage is only around 60% for both cards.

On Ultra settings my GPU usage jumps up to 75% for both cards, CPU still close to 100% and I get some major stuttering sometimes down to 1 fps during some major explosions.

In both cases my RAM usage is up to 85%.

With single card CPU drops to 85% and GPU is at 100% and everything becomes much smoother.

My current theory is that it's a CPU bottleneck, but I don't know how to prove that. Nvidia does PhysX inside the GPU, but with Radeons it gets offloaded to CPU, this what led me to my theory of CPU bottleneck. BF3 will be my main game for at least a year and I don't really want to buy a whole new system. I could spend up to $500 to upgrade, but do I spend it on 2500k/MB combo or Nvidia 580? And is there anything else I could to diagnose the issue?

My system:
Asus Crosshair Formula 3
AMD Phenom II 955 (OC 3.7 GHz 18.5x200)
5870 x2
4GB 1600 Mushkin 7-7-7-21 DDR3
Win 7 64
1080p LED TV
700W Cooler Master PSU (52A on single rail)
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More about 5870 crossfire problem bottleneck
  1. If you possibly can, try and get that cpu up to 4.0 ghz. And see if that helps; otherwise you may need an upgrade.
  2. Unfortunately I can't OC over 3.7. I have tried multiple times, I think it's just one of the worse chips.
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