RE: NS X_type Vs. Natural
Not sure it will help you, but I had the Transam 6.0 and the Tonix 5.8 (ancestors of the X-type and the Natural respectively). The Transam was more stable and faster, so might be the X-type vs the Natural. Both sails lack low end power in ~ 6.0 but they can take huge amounts of wind. I gave the Tonix away afer one year. I still use the Transam in conditions where I was using a 5.0 sail in the 90's, so 6.6 might be the right size to replace your Edge.