I had the 1991 and received the MoFi yesterday.
A bit clearer with bit more space around instruments. Vocal slightly larger. The guitar rifts were to further the left of the sound stage.
I would say, for me 5-8% change/better based on playing them one ofter the other.
The end result is I'm glad I purchased the MoFi.
I will probably look for the SHM. I have a couple of other SHM, and they are very good. If you asked me which ones right now I would need to go look through the shelves to see. Old and fading memory.