I have a different perspective of the 617 now that I have the SDL.

The 603 can warm itself up to 100°C. when under moderate boost, with the a/c off.

However, with the a/c on, it will have a difficult time getting over 105°C. even on a long upgrade.

So, look at the situation this way:

The 603 has no issues at 105°C. and it has an aluminum head.

Therefore, all you folks with 617 engines can relax and worry about other things. You can probably run the 617 up to 120°C. if you have proper coolant and sufficient pressure in the cooling system.