After a period using my HS 5870 I switched over t0 my EII flashed HIS HD 7950. The 7950 is in PCIe slot 1 In Sierra 10.12. 6 Link width = X8. Link speed = 5.0 GT/s In High Sierra 10.13.0 Link width = x16 Link speed = 5.0 GT/s ( About to upgrade tonight to 10.13.4 ) Anyone have any thoughts why the Link width shows as x8 in Sierra ? Sierra bug ? EDIT : Oops ! I should have put " LINK WIDTH" in the thread title.