Between five and six meters seems to have been something of an international standard for pike lenghts. Macedonians, medieval Europeans, the Japanese, all ended up averaging about five and half meters. Longer ones past that "critical mass" apparently proved to be excessively heavy and unwieldy and, so I've been told, started sagging too much under their own weight and lenght.

And you know, it does look kinda silly when the little RTW soldiers wave theirs with one hand...