I would get the 1333mhz one. In the MacBook Pro, they use 1333 but 1600 was compatible with it. However, I would recommend sticking with a 1333mhz memory set mainly because it honestly doesn't even make a BIG deal.
Yes the number is the speed but it will fall back to 1333mhz, if you are buying Kingston ram, I would buy this KTA-MB1333/4G two of these will give 8gb with the 4 already installed you'll have 12gb. the hyper X will do nothing for you but cost more.