What's the difference between the Sulky 30 weight and 40 weight Rayon threads?

The lower the thread weight number, the heavier the thread. I know that makes no sense, but it's the truth. The 30 weight thread is approximately 1/3 stronger and denser than the 40 weight thread. Most of the computerized embroideries today are digitized for 40 weight thread. However for decorative topstitching and quilting, the 30 weight shows up more.