Very fine machine. I recently got an SG1 with Congress elite type, like this, which has become one of my favorites. I note that your SM4 has carriage release tabs on both ends of the carriage, which is a very desirable feature in my book. I wish I understood the S/Deluxe designation better.
Beautiful typewriter - delicious. The keys look like a box of chocolates. The rounded typeslugs are a neat detail I will look for in Olympias in the future.
I can only speak to the "normal/S/Deluxe" differences as stated in the 1962 SF model parts book, which shows the rounded-body SF and SFS models differentiated mainly by the S model's plastic paper guides, touch control and about a 1 page list of parts differences. It shows the "SF Deluxe" model with the newer angular shell and another page of listed parts differences. Also, of course the different segment cover plate - one blank, one with the "crown S" logo and the last with "Deluxe" engraved on it.