There are really only three major types of metal used in audio stuff,
M6
50/50
Permalloy (80Ni)
Lam thickness is usally always 0.014 in., unless it is a cut C core like Langevin output, which uses 0.004 mil steel.
Some folks add Cobalt for low end, others think this slows down the high end.
Mag Metals has a Cobalt lam called Super Q.
It has less distortion, according to the lady at Mag Met.
Supermendur is used mainly in power transformers.
It contains Cobalt also. Takes more flux per pound.
Good for airplanes.
Flux densities are usually listed in the lamination catalogs.
FIgure out where the core is going to be running and adjust up or down.
Adding a bunch of iron does not guarantee a better transformer.
As soon as you change one thing, some other parameter will change.
Like core loss.
0.014 is easy to cut.
0.011 bends a little too easily.
Usually the 0.011 was used because the steel was not as good, so the thinner lams make up for core loss caused by low silicon content.
It is a lam thickness from the old days.
I use to cut 0.011 and it was a pain in the rear. Folded up like a house O cards when going thru the machine.