I crossed mine at 100 Hz and I assure you that my subwoofer was not directional. The M3s driven by a 5 wpc SET tube amp and Velodyne sub created the much desired wall of sound effect.

The point that speaker performance in an anechoic environment will differ from real world performance in your room is well taken. Rather than take anyone's advice, you may want to put some time in to tweaking your system in your environment for your pleasure.

Enjoy the Music. Trust your ears. Laugh at Folks Who Claim to Know it All.