The conduction velocity of the squid giant axon can reach 30 m/s. Is there any known example of an even faster conducting unmyelinated axons?
The conductance velocity in the unmyelinated axon has been calculated and measured to be proportional to the square root of the axon diameter (see for example: Rushton, 1951). Since the giant axon is, well, giant, it conducts much faster than others. AFAIK, all other large neurons studied are myelinated. Maybe try to find bigger squids! ;)