Question: How low can your power go if you halt the PPs and the MP? for both C80 & C82

Answer:
For C80, an empirical estimate is ~1.4W
For C82, a good estimate is ~1.2W.
This is not as low as you might like, so again, unless there is a major reason why you don't think gating your clock with an interrupt which enables/disables clock in, we believe gating is the best solution, and can bring power down to virtually nothing.