Damn how'd i miss this?
ok. yeah. really the peak of the machine's power seems to be Low 2-C due to the machine and his brother the maker.
The Machine is a metaphysical entity which exists between what is real in Nevada, which according to The Disquieted One controls the actions of every single nevadean. Without the Arena Mode player, the machine will break down destroying the (stated multiple times as mentioned in this thread) infinite sized nevada releasing unknown horrors in a hellfire.
With the existence of his brother, the maker, it proves that not only does the machine have the constructive capacity to destroy the universe, but it also an implied helping hand in it's creation as the maker mentions him not creating nevada alone.
It's basically the universes' biggest shaken can of soda. if it explodes everything gets a little messy. It pulls the strings of the universe, and without those strings the marionette falls.
you could theoretically do a possibly 2-C at best if you mention the fact the maker likely created purgatory, which would give him a whopping two universes created. but thats the highest i see them going.