Yes, I have experience with sound deadening materials.  And to some
degree all of the info you have is correct, though I'll never believe
that McMasters supplies dynamat.  The product that I came to that was
the best combo of price and effectiveness is RaamMat.  It's a deadener
supplied mostly within the industry of sound competitions by one guy
named Rick McCallum in San Diego.  You can buy it through his website
now at:  www.raamaudio.com  His top of the line mat (called BXT) never
really blew my hair back, but the others like original raammat and
raammat 60 are second to none.  Easy to apply, sticky as hell, and dead
quiet.  By the way.  If you are a member of carsound.com you get a
pretty decent discount.