With a very small compromise, thermal bridge, of adding plywood to tie the tops of inner & outer stud walls, tying them together at their tops, I can make my "dream house" airtight without insulation or drywall.  This is true because I'll need OSB on the ceilings to support the insulation anyway.    This would make my primary air barrier the exterior sheeting, windows doors,  basement and ceiling OSB plus this wall cap.  My walls will be r40 and 9 feet tall so the effect, of the 1/2" OSB wall cap, will be to reduce whole wall r from 40 to 39.5.   I'm thinking this is a very worthwhile change since far more heat could be lost through air leaks and they will be much easier to locate and fix before walls are filled with cellulose and drywall hung.  Not using all the gaskets & care to do airtight drywall also make up for the very small cost of tying the walls together.  Your opinions please.

Duh,  After a little bit of thought: Why not cut pieces of 1/2" foam & lay them over the outer wall top plates between trusses. this would accomplish the air barrier completion without adding a thermal bridge.