Hi Charles, :D
Having tried both SMs and Mules in my Les Paul Standard, I can confirm that the 'standard' AIV Mule is also sweet sounding - albeit with a bit more clean 'push' if you need it - notably with more midrange than the SM. It is still not compressed though, so you will get that lovely open sound from both.
Both are lovely pickups - and if you play a lot of clean ( like I do ) both work nicely. I gather the 'Mule' is closer to the original sound of a late 50s PAF - and the SM an early 60s.
It must be lovely to have a Les Paul with both types in together, especially using the combination of pickup positions you are considering ! 8)
I used to play a standard LesPaul with a pair of Mule Alnico IV, the sound was louder (with mid) and it is a pleasure to play it "Rock". But the Lespaul artisan is totally different (acousticaly !) and the fretboard is ebony with wide and low frets, so I play differently ! Yesterday, I compare both guitars on a Marshall JTM45 Reissue, and the LP std was very "mid range" and had some crunch. But the LP Artisan was very clean, the neck PU was jazz/funk and the bridge was bright but not loud enough to crunch.
So, if I want the same bridge sound with more level output, should I choose a Stormy monday Alnico IV or a Mule Anico II ?
ps: excuse my english, I'm french ...