Stepping very gingerly into this one.
I looked at the link above where they refer to the ASHACE. I have never heard of this organization, though the initials are certainly close to ASHRAE, an organization I belonged to for a few decades. Looking thru my long list of professional and industry organizations, this one doesn't appear anywhere. Make of that what you choose.
The link also concludes that all the building codes are going to change their guidelines based on the performance of their insulating product. Sorry, but it just doesn't work that way.
They also distort the reasoning behind a vapor barrier in a convoluted argument over summer cooling.
Again, do as you feel best, but be aware that ASHRAE performs considerable research every year into issues such as this, and that research is used (along with other parties input) to help formulate building code requirements such as minimum insulation values.
I would also recommend that you consider anecdotal information and user comments and opinions with due caution.
As to insulation amounts, follow the manufacturer's recommendations. Excessive amounts of certain insulating materials not only are not cost effective, in some cases can actually degrade the final insulating value. The best approach is to treat any building element (wall, ceiling, etc.) as an assembly. Calculate the insulating performance of the assembly, not just the amount of added insulation. And despite some very vocal critics to the contrary, an effective vapor barrier is indeed recommended.
Offered only as opinion
