All I know is that it has been recommended (or stated?) that Airstream uses 616 exclusively. We are doing our first Vulkem repair, so have no experience in difference. Maybe someone else who has used either/both will respond, but we will go for what is suggested for now.
Leigh (IB Aluminated)
"When a great ship is in harbour and moored, it is safe, there can be no doubt. But that is not what great ships are built for." by Clarissa Pinkola-Estes, author of ‘Women Who Run With the Wolves’