I think you have to consider the volumn of heat in this case since the exhaust gas is flowing through the pipes. If it's not transfering as much heat through the metal because it transfers slower then more is going out the exit. Not ultimate temp but volumn of that temp.
It's a dynamic situation. Air is flowing through the engine compartment to carry away heat. If the heat is being transfered more slowly by the stainless then the air will have more time to remove that heat and stay ahead of the transfer.
It's a dynamic situation. Air is flowing through the engine compartment to carry away heat. If the heat is being transfered more slowly by the stainless then the air will have more time to remove that heat and stay ahead of the transfer.