Just wanted to note again a comparison between Scald and Rage Potion in terms of Steam Machine.
In the all-upped scenario, a single Scald indeed quickly (after 4 turns) overpowers Rage Elixer, as well as being cheaper by 1 quanta. However, Rage Elixer can be used repeatedly on the same Steam Machine, while extra Scalds will become dead cards.
However in the all-unupped scenario, Scald is clearly inferior to Rage Potion. You can only use "steam" twice before you kill the Steam Machine, meaning that the most you can get is +4/-4, which is less than Rage Potion's instant +5/-5, and there's no limit on the amount of times you can use the ability.