[TowerTalk] material permeability of a BalUn core

[Kostas SV1DPI]

I am reading the book "Understanding, Building, and Using Baluns and Ununs"

In the page 37 refers to 1:1 baluns. So it recommends that the core of a 
Reisert balun (current balun) should have a permeability of 250 (160m) 
or 125 (80 to 10m) or 40 (20-10m) for maximum efficiency. I have seen in 
several articles that some guys make their baluns using mix 31 ferrites 
(2631803802 has 1500) or ft240-43 (permeability=800). As I can 
understand a higher permeability means a better chock or not? According 
the book I gain efficiency with lower permeability but what I loose? 
Have something changed after the book is written or not? Comments please...

73 Kostas SV1DPI