Exhaust sizing

Personally I use this site as a guide. The guy goes through the math showing you how he arrives at his figures. And the math makes sense and adds up. But the quick guide at the bottom really sums it up nicely. Obviously this is probably more aimed at WOT in terms of how much flow you need. But really, why restrict something that you KNOW should flow as freely as possible?

http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/