Great stuff Andre.
That article was written in 1964, and there are now some very good software tools for doing all that.
Check out the Micrometals website.
**broken link removed**
There are several things you need to think about, but with most toroidal chokes the problem is one of core losses due to ac induction, which rises steeply with frequency and ac flux density.
But the magnetization curves and loss curves are all there for various core materials if you wish to go through the whole long iterative design process yourself.
The Micrometals design software allows you to punch in some numbers and it will give you a whole range of possible solutions.
These toroids are both economic and excellent where the ratio of dc current to ac voltage is quite high.
But they make very lossy ac inductors at high frequencies and for high applied ac voltages.