An example where Knuth-Morris-Pratt Algorithm is faster than Boyer-Moore?
There is a paper that did a good experiment over these string matching algorithms for different patterns:
"Comparison of string matching algorithms: an aid to information content security"

Also there is a study of these string matching algorithms for Japanese language:
Comparison and Improvement of String Matching Algorithms For Japanese Texts

I hope these are useful to get a sense about algorithms efficiency!