If spec is for 1866 or above run at spec 1.65 and spec freq, while many buy and use 1.65 sticks they are gradually getting them out of the inventory - Kingston and Corsair continue to offer sets of 1600 at 1.65, I myself won't use 1.65 for anything under 2133..I doubt it will hurt your CPU, but 1.65 is just to much for entry level 1600/9 sticks