Ever since I thought about the Iron Amenia Savant, I've just been thinking about the parallels savants have with drugs and dependency. The two good examples of Allomantic savantism we've seen in the text, Tin and Pewter, seem to cause physiological changes in the savant. I'm pretty sure most other metals would not be nearly so dramatic since Tin and Pewter are internal metals that directly affect the body and thus would be the most visible. Metals change the part of you that they would otherwise work on (Cognitive, Physical, Spiritual, and Time), either deadening (Pushing) or amplifying (pulling) the thing they affect when burned. I'm assuming the internal metals have more dire problems since they directly shape your spirit web instead of affecting it from the outside, as most of the external metals do. I just hope that External savantism has a sort of feedback effect from burning it too much. Otherwise, I have no idea how it works. Additionally, all the savants we see have a dependency on the metal, with them still needing to burn the metal to function normally. I'll also draw on the other metallic arts for inspiration as well as larger cosmere trends. (Spoilers for size) Also like don't question the order of them.
PHYSICAL
MENTAL
ENHANCEMENT
TEMPORAL (This the one I'm most unsure of)