Graphite is a carbon it will burn, it will not handle flux well, its cost is a lot higher, for torch melting I feel it would be burnt easier by the torch, in a furnace without flux where heat is more even and if melting pure metals it may work well, graphite also being carbon based could reduce base metals where silica would not and base metals may be oxidized in the oxidizing flame of the torch in a melting dish.
I am no expert on this these are just some of my thoughts, I can buy a three dollar silica melting dish and melt several ounces of gold with no problems, and reuse the dish for melting other metals with, if I want to melt a metal with flux I can, if the flux attacks the dish a little I have not lost anything.
