Char here. A BoM would give about 900K ST and a good amount of enc, along with a small amount of AC, whereas a MgS would add an additional 30% protection on top of the 26% from my RoBF, bringing the total reduction to about 48.2%. On the other hand, by doing so, I forfeit AMF, and thus become extremely vulnerable to decay. (My AMF is about 500K.)