Here's what came out of the article on the 4-2-1 vs 4-1:
CONCLUSION ABOUT HEADER DESIGN

So the old adage that 4-1 = more peak hp with a loss in midrange torque and 4-2-1 = more midrange torque with less peak hp is an obsolete idea.


Newer hybrid headers of the 21st century are a fusion of the old 4-1's extra length with the 4-2-1 layout, have stepped diameters, and have large diameter collectors. So you have low end peak torque with enough breathing capacity to support more peak gains (the best of both worlds).