Do you think they achieved that performance optimisation with a networked service because they switched from insertion sort to quicksort?

I did the same thing in PHP before. Issue was a foreach over a foreach with a search. The fix was to build the result set as you populate the main array of objects. Basically as you add stuff to the array if there's a value that matches you throw it into another "results" array for any cardinality (unique value) that exists. Since in PHP objects are always just pointers your results arrays are relatively painless. Just a series of int32 integers basically. Then when you need an answer your result is instant. I ended up getting a 80-90% speed up. This is not just a php thing either. Folks end up doing this type of stuff in every language.