A “slowing down” of a simulation would only be perceptible to those observing from without, not those who are observing from within, whose perceptive processes would be slowed in synchrony with the processes they are perceiving.

There's no reason to presume the simulation proceeds at a constant rate as measured from the outside world either: “render times” may vary with the complexity and fidelity required — for example when we innards fire up the LHC, a huge bump in resolution might be required. When we innards venture onto the moon, a whole new world has to be mapped in and professing speed might drop accordingly.

What the original poster is saying is that insofar as we do not know what the base reality is, there is no reason to argue that our reality is a lower-fidelity instantiation of it: we might as well be a flawless emulation of something totally orthogonal to the base reality.

Furthermore for obvious reasons computation cannot endlessly recurs endlessly and somehow forms into a loop: somewhere the arithmetic actually has to be performed.