Interesting question indeed.
My Stormy neck is 7.1K, while my Mule neck was 7.3K. So, not much of a difference there. Both are AIV magnets.
With that being said, the differences between the two are fairly profound. The Mule, despite hardly any difference in strength, was much easier to drive than the Stormy Monday. The Mules bass response was also significantly stronger than the Stormy Monday. The Stormy Monday is very crisp and clean, very even string response. Almost a "pop" bass response, very tight and clean. It has a certain airy quality when overdriven.
The Mule was a better "rock" pickup, very versatile, while the Stormy Monday is better for blues, jazz, and blues leads.
The two best neck pickups I have ever played, but very different despite their structural similarities.