Interesting. I knew most of that more or less but didn't know the mechanism by which the myelin sheath speed up the propagation of action potentials but it makes sense.
Hodgkin and Huxley, who figured out how the basic mechanism underlying action potentials, worked on the squid giant axon because it's so large, up to 1.5mm in diameter. And the reason is large is that invertebrates do not have myelin, and the large diameter helps speed up signals:
https://en.wikipedia.org/wiki/Squid_giant_axon