Did you notice that those CPus are scoring better at BCLK204?

The CPU-score for:
@5.21GHz(204x26) = 73338
@5.44GHz(210x26) = 73039

Those babies hit a wall at around BCLK203. This wall may vary depending on the system, but it seams to be cased by some limitations in 5220-chippset and IOH. In case, it can reduce the GPU-score too.

have you tried the quad GTX580 at BCLK203? if not, it would be interesting to see if you get a better CPU and GPU score then.