Sounds like the miner is properly using the CPUs at least, that number means 90-100% usage across all 8 cpus. I think recompiling with the latest libgmp is your best route.

I'd hazard a guess that it's not properly threading the CPUs, as you get similar pps as my i7-920 @ stock. AKA it's running your 8 4 core CPUs as 1 8 core cpu.