Steel stud wall insulation stack up question – GreenBuildingAdvisor

I have some steel stud interior partition walls going in a building (climate zone 4) that has zoned heating/cooling. I would like to handle the insulation properly.  There are basically two types of walls:

A.  Walls that divide conditioned space from conditioned space (might be a moderate discrepancy in temperature based on zoning).

B.  Walls that divide conditioned space from “roughly” conditioned space (ie 45F in the winter, 85F in the summer).  

With the steel eating up so much R value, I figured going thinner on the wall (2.5″ where there are not doors and 3 5/8″ where doors are present) and adding a layer of foam was advantageous.  

1.  Which side of the wall should I put the foam in the two scenarios above?  Does it matter?  

2.  To me, it seemed like 1″ of XPS would add significant R value (and vapor retarder + air barrier) without making drywall installation too difficult.  Is that typical for interior walls?