KiwiTim: You could always try flashing the BIOS with the latest release for the motherboard.
I once had a motherboard which had the latest BIOS release installed, but this had been done several years back. I reflashed it with the same BIOS version and it performed much better. The BIOS must have become corrupted some how.
Of course, if you stuff up the BIOS flash your motherboard could be ruined, so there is some risk ... but its never happened to me.
Done that too. No difference