I think the issue is with the Bus Mastering. the intel 82579 doesn't support it. it takes the interrupts from the CPU. and somehow the new drivers just shows it or might not enable it and have worst performance.
The CT has the Bus Mastering enabled always but has crap performance with the new drivers too, from intel drivers or from windows update drivers, it's the same since 19.5 or something, I think 19.1 works fine, can't be sure already.
