I just looked up the i7 3770 and the fastest speed RAM it supports is 1600MHz. If you are getting very near to the top of your RAM limit then you can consider getting more RAM. But if you get anything with a faster speed it will be underclocked to 1600MHz effectively wasting the money used to make it faster.
Also, RAM speeds don't even make a noticeable difference in performance. They do make a difference if you can upgrade but you'll never see it.