With a cathedral ceiling you get one chance to do it right. Put in the max. Stuff in 6" of fiberglass then add as much foam below as you can afford, then add a bit more. I'm in Manitoba, Hydro is recommending R50 now. I put in R60 two years ago. Yes R-Six-Zero.
As for economy and the 95% - 96% boys, where were they years ago when R12 was enough, then R20, R40.
The cost of heat is only going to go up. The bean counters will whine today because "You won't get the return for your money" then tomorrow they will cry "It costs so much to heat, put in more insulation". In reality that bunch doesn't know their ass from a hole in the ground.
If you are building to sell and make a quick buck then go bean counter minimum, otherwise think 20 years down the road. If not for yourself then for your kids if you want them to be able to afford the place.
Lots of ventilation. I put in metal ridge vent right across all three sections.
One added bonus of the metal ridge vent is that birds don't like to land on the things. they stay away from my roof and crap all over my neighbors roof (ridge vent covered with a shingles) Seagulls, crows etc. the stuff covers half the top of his roof and hardly a drop on mine .
By the way I built that place, I hired out the foundation, shingles and HVAC, the rest I did with help from family and friends, not a fricken bean counter among them. :) :) :) and as they say "Put my money where my mouth is".
LdB