First, without knowing the makeup of files he has, you can't tell how much a corner case this is. It could be 100K small files or 10 large ones. Few care about runtimes for small files, but many care about runtimes for large ones.

Also, and probably more importantly, you'd use ack differently in a recursive-find situation. You just "ack" from the top of the tree. The perl interpreter starts only once.

I don't think this is a useful benchmark for typical uses of ack.