so was it a driver issue in the end? im curious b/c we run 10Gbit at work over iSCSI. it's a similar setup as yours w/ SFP+ copper. I dont believe ive seen any numbers that low, but we dont get anywhere near 10Gbit (not expecting to).
i remember GA boards have some ctrl+F1 'expert' mode where you can then tweak individual settings. from what it sounds like, you'll have to manually tweak the settings and probably unstrap the memory from the CPU im a bit rusty on the details - i havent tweaked a BIOS for years now.