From all your good comments, I decide to choose between the followings:
1) G.SKILL Ripjaws X Series 8GB (2 x 4GB), 1.5V, 9-9-9-24, 240-Pin SDRAM DDR3-1600 (PC3 12800) Model F3-12800CL9D-8GBXL @ 96.99$ per set.
2) G.SKILL Ripjaws X Series 8GB (2 x 4GB), 1.5V, 9-10-9-28, 240-Pin SDRAM DDR3-1866 (PC3 14900) Model F3-14900CL9D-8GBXL @ 126.49$ per set.
Those prices are so good that I will buy 2 set of 8GB for a total of 16GB and I think I will take the option 2.
Thank you very much for your help