Very interesting info here:
http://superuser.com/questions/812022/force-a-single-usb-3-0-port-to-work-as-usb-2-0
and here:
http://www.intel.com/content/www/us/en/chipsets/7-series-chipset-pch-datasheet.html
and here:
https://downloadcenter.intel.com/Detail_Desc.aspx?lang=eng&DwnldID=10316
and lastly, here: