I've probably read a dozen different articles on back pressure and they all end with the same conclusion;the faster you get the spent exhaust gasses out of the system the better(providing your system has the correct pipe diameter(s) for maximum scavenging).If you find something to the contrary be sure and post it up as i'd like to read it.
It's a good article. However, the garden hose analogy that he uses is misplaced.
With the garden hose analogy your are restricting only the end of the hose - i.e., you have a large diameter tube of considerable length and putting your thumb over the end accelerates the flow due to the Bernoulli principle. The same principle that causes airplanes to fly.
When referring to exhaust systems, he's talking about restricting or enlarging the size of the entire length of the exhaust pipe not just the very tip of the exhaust. If you were to take an entire garden hose and restrict the size of the entire length to say that of a soda straw, the velocity of the water coming out of the end will be no where near as fast as it would with a standard garden hose with your thumb over the end. The friction of the water traveling through a soda straw size hose of the same length as a garden hose will slow the water down considerably.
Hopefully the use of this analogy is the only thing in error in this article.
Hopefully, someday soon. Right now my only free day is Sundays and it's usually filled with stuff I couldn't get done during the rest of the week. But, you have to make hay while the sun is still shining. When I do ride on Sundays, I keep it close to home so I can still get some stuff done in the afternoon. I'm hoping things lighten up in a few months...