Hello and welcome Scott.
As one that does not do a lot of bright cutting here is my take on it.
The bright cut is a function of the degree of fine polish applied to the graver.
Not on the graver material.
That said, the Cmax being harder will probably continue bright cutting longer than HSS providing you don't chip it.
the critical factor is the degree to which the final polish is taken to. whatever the tooll is made of, well, i have never seen a difference in the work i have done.