The problem often seen in "low power pipedreams" is that significantly lower power can only be realized if an outside event can trigger the active mode. CMOS yses "no" power when static, but a timed wake up requires an oscillator and counter etc.

So, with a bit of exaggeration:
you will not see a large advantage in sleep/power down modes unless you can use an external event (e. g. someone pressing a key) to start the processing.

Erik