Determining correct target R value for wall – GreenBuildingAdvisor

I have a large building (zone 4) where the bottom 54″ of the wall is a concrete stem wall, while the rest of the wall (18ft tall) is a steel framed all.  I am trying to determine a good target R value for the wall above the concrete.

The plan is to insulate the concrete stem wall with rigid insulation before installing a veneer, but I only have the space on the outside to go so far (roughly 1″ or R5).

Is there a good rule of thumb for R value targets in situations like this?  In case it matters, the way I am currently building the wall with rigid exterior and cavity fiberglass insulation, I expect to get to about R12.