Climate Zone 4 Building Question – GreenBuildingAdvisor

I am building a Pretty Good House in Southern Missouri, Climate Zone 4a.

I want to start off by saying I have read the Golden Article regarding the amount of rigid foam exterior insulation here: https://www.greenbuildingadvisor.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing

My projected wall assembly from interior to exterior is as follows:

5/8 Drywall > “Smart” Vapor Retarder > Fiberglass Batting (2×6 cavities) > 7/16 Zip, Taped > 2″ Foil Faced Polyiso

I am at the stage of filling the cavities and putting the drywall in. My question stems from a moisture sandwich. I am worried that the vapor retarder/barrier will be too much blockage to allow good drying potential. As I understand it, the painted 5/8 drywall will act as a vapor barrier.

I did not follow the ratios laid out in the article, as he even says that for my climate zone, the sheathing will never get cold enough for condensation issues anyway. 

So my question is two fold. 1. Should I even consider a vapor or air barrier inside? 2. Has anyone had experience “over insulating” a wall?

Thanks in advance!