I have three S&M, all in ATS34. Great knives. S&M uses 420HC because it gets a nice shine, much better finish than the D2. It also holds a decent edge, at least as good (I think better) than SAK steel. In the past D2 would not be a good steel for the S&M line since it does not take a high polish. However, IIRC I believe the new owners of the brand have some S&M in D2 and even (horrors) 1095. If I was them, it would be all 440C and ATS-34/154CM.
The S&M patterns are sturdier than Queen (I have a Queen and S&M toothpick) and have more embellishment such as swedges, pinched bolsters, etc. plus better bone and stag. There used to me more discussion on them in the past. You don't see them much on this forum, because everyone loves GEC and IMHO the current S&M owners have not yet decided what to do with the brand.