I have a Sabertooth x79 and 4x4gb of Gskill Z series RAM. I went with the Z series because on the Gskill site and on Newegg is said this RAM was designed to work with the 2011 mobos. In my mobo manual, the QVL lists the X series version. The X series according to Gskill and newegg are for the 1155 mobos. So which is the correct one to use? I am getting errors on memtest with my Z series RAM. Already RMA'd once. Still receiving the same errors on the same test. Test 6 every time.