Typically the higher models are the cartidges that measure the best. In otherwords, the cartidges are made then tested. The cartridges that measure good are the expensive models and the cartridges that don't measure good become the cheap models. They measure for frequency response, balance, separation etc.
Explanation of what higher costs buy with Grado
Can anyone give an in depth explanation of what one gets with increasing costs in the Grado woodies? Their website is remarkably vague. The only differences between the Sonata, Master 1, and Reference 1 listed on their website is an elliptical stylus in the Sonata & Master 1 vs. an ellipsoid stylus in the Reference 1. With the steep slope of the price increases between these three models, one would think that there has to me more than a difference in stylus profile.