I'm not wild about the labels "implicit" and "explicit" for mental models. "Explicit" is not bad, but "implicit" is less intuitive. IMHO, "behavioral model" is a better label.

With simulations (e.g. CPUs), what the OP referred to as an "implicit model" is a "behavioral model" (the results are right, but the simulation takes shortcuts). An "explicit model" is a "cycle accurate model" because the simulation goes through all the actual motions that the real target (CPU) would do.

Behavioral models are much faster but less detailed and sometimes less accurate. For instance, in a CPU simulator, you get estimated execution times for the code whereas for a cycle accurate model you will get actual (simulated) clock cycles that the instructions took to execute the code.