It's sufficient for my purposes just to show that "bit" in a logical model and "bit" under some idealised thermodynamic thought experiment are radically differe

It's sufficient for my purposes just to show that "bit" in a logical model and "bit" under some idealised thermodynamic thought experiment are radically different notions. Reality, i am sure, has many systems which are settable and measurable and changeable at some minimum energy... and which can interface with devices of interest. For any given problem, the limit case energy requirement is defined by the needs of the algorithm. If we require setting a highly complex input state, and if we require interactions with certain devices, then we've immediately ruled out a great deal. These systems would provide you with a certain kind of "limit-case correspondence" between "logical bits" and "ideal physical bits" --- but we dont know what this system is. You dont get it from just playing around with units, nor these kinds of thought experiments. You need to know what algorithm you're talking about, and what it's requirements are. If the algorithm is understood just to be "the whole of reality" and if we suppose that it is fundamentally just aggregates of discrete states being flipped (to me, highly unlikely).... then the energy requirements are Everything... which sum, i imagine (via energy conservation), to zero.