Dear Nandric: I can't understand in a precise way what you mean by cartridge " iron bobins ".
Perhaps you are reffering to the cartridge armature where the coils goes on.
There are different type ( like you say ) bobins like cross-shaped, v-shaped, square-shaped, etc, etc.
Fron the point of view by some cartridge builders the non-magnetic/non-conductive cartridge armature build material is more linear, example: Ortofon in its top of the line MC cartridges use carbon-fiber material.
IMHO a cartridge quality performance depend on many design factors and the execution quality on the design, I think that there is no single/aisle cartridge design factor that could define the whole cartridge quality performance but the " wise " choice/synergy of all cartridge factors in the final design/build product.
+++++ " The advantage: stronger signal and some kind of 'pleasing warm sound.the disadvantage:(more)distortion. " +++++
if that is true that is a trade-off like almost always in any audio item design, which cartridge trade-offs design/build are the best?, well which quality cartridge performance do you like more.
Now, IMHO I think that other than a direct cartridge builder ( like Dynavector or Scan-Tech ) the right person in this analog forum to give us an in deep explanation on the subject is JCarr, I hope he can share its knowledge with all of us.
Regards and enjoy the music.
Raul.