Vapor permience and wall drying potential – GreenBuildingAdvisor

Hi Everyone,

Long time reader but first time posting. I am currently working on a new house for myself in an area near Edmonton Alberta Canada. For simplicity for my framer we are doing a standard 2×6 wall construction with 1/2″ plywood sheathing and then I am doing a SA WRB, 2″ of comfortbatt 80, and a rain screen. 

I am a little bit torn on my WRB selection when it comes to vapor permience. With this wall assembly in my climate because I am not going 50% of my insulation value to the outside I want to ensure as much drying potential as I can from within the wall cavity outwards should there be a need for it. I am stuck between using Henry VP100 (33 perm) or SIGA Majvest 500 SA (16 perm). Will the higher perm rating of the VP100 even make any difference due to the vapor permience of the plywood behind it? I am also considering whether it is worth going with one of the SA products or am I better off just using something like a SIGA Majvest 200 instead?