I recently implemented lightsleep/deepsleep for CircuitPython and also tested the Pico-Plus2 and Pico-Plus2-W.
Both perform quite good: I measured about 1.4mA in dormant mode compared to about 1.8mA for the Pico2/Pico2-W. This doesn’t sound much, but if your duty-cycle is low (i.e. your system is mostly sleeping) this is a power-saving of more than 20%.
The RP2350 uses a low-power oscillator (LPOSC) for dormant mode that can wakeup the system with a timer. The RP2040 did not have this feature, so timer-based sleeps used much more current on these old chips.
There is one caveat though: the LPOSC is not precise, and the precision depends on voltage and temperature. The net effect of this is that the sleep-times of the Pico-Plus-2 is 25% off (i.e. if I request 60s sleep it will wake up after 75s). The Pico-Plus-2W is off by 17%. On my specimen at least. My Pico2/Pico2W test-units are off by 1% and 5% respectively. No idea if the better performance is related to this increase.
@ZodiusInfuser, @gadgetoid: asking the real gurus: any thoughts?