Well, I find it hard to believe that a built-in perl function that has been optimised and is written in C should be slower than walking through the array yourself... (ie. doing the exact same thing the built-in is supposed to do). It is contrary to my own experience, at least. Plus I find myself too lazy to write and debug own code when I can use a built-in :).

If you really have reason to believe what you've heard, why not just quickly whip up a benchmark.