Idea for an essay?

I’m doing an essay on sorting algorithms (more specifically insertion sort, selection sort, merge sort, heap sort and quicksort). I’ve written most of it but I need a specific subject (I know, I kinda inverted the procedure, long story). Right now the subject is “comparison of the performance of different sorting algorithms” but my teacher told me it’s waaaay too broad and that I need to narrow it down a lot more. Anyone got an idea?