Vapor barrier on interior with rigid foam exterior – GreenBuildingAdvisor

I asked a similar question a while ago but got a little off-track and broad with my questions:

Kraft faced insulation Va. poly vapor barrier

My question is this: 

I have the wall cross section as shown in attached picture:

1.  If I use sheetrock (painted with latex paint) for the interior wall covering, is a vapor retarder over the cavity insulation a benefit or a detriment?

2.  If I use plywood for the interior wall covering, is a vapor retarder over the cavity insulation a benefit or a detriment?

3.  Kraft paper has a perm rating of 1.0.  This is about the same as 1″ of XPS foam (perm 1.1).  Would these work interchangeably underneath the drywall or plywood?  I would not mind the extra R value of the foam if a vapor retarder is needed anyway.

Thanks in advance.