Funny thing is, I tried to install PC3-10666 on a Lenovo 575 which previously had PC3-10600, and It wouldn't take. Computer wouldn't even turn on. However, I installed the same ram on an an HP DV7 laptop which is rated for pc3-10600 and the 10666 worked just fine. I guess it's a toss up.
Was the new memory the same timing and voltage as the memory that was already in the machine?