What does the dual rating listed on circuit breakers mean? (60/75) Is it just indicating a range of wire sizes that will legally fit into the terminal, or is there more to it?
If there is a choice, most people would probably choose to use the 75 deg rating.
thank you

This should indicate that the terminal is listed for use at either temperature ampacity. If the teminal was only listed for use with a 60 degree termination it would affect the wire size you could use to achieve the required ampacity. See Section 310-10 and the associated Tables to see the affect of the different ampacities in the different temperature columms.