It's not about speaker quality, its about the sound quality that your speaker produces.
If you take away the higher energy demands of the Low Frequency reproduction, then that energy is focused at and above the XO frequency. By experimenting with different settings you can determine what sounds best. In my case, I started at 60, but when I tried 80, the Mid-range clarity picked up... subtle but definite. The bass response also improved, as the lower frequencies were passing off to the Sub a little sooner.
Setting your XOs is a balancing act. Ego is not part of the equation for a successful setup. I have Mains that can go into the upper 20s... I still cross at 80. Why? because the performance increase is noticeable.