Not sure you can wake up from sleep with PCINT. Think you need to use one of the external INTs for that.
Yep, have a project that does exactly that. From the datasheet:
10.5 Power-down Mode
When the SM2...0 bits are written to 010, the SLEEP instruction makes the MCU enter Powerdown
mode. In this mode, the external Oscillator is stopped, while the external interrupts, the 2-
wire Serial Interface address watch, and the Watchdog continue operating (if enabled). Only an
External Reset, a Watchdog System Reset, a Watchdog Interrupt, a Brown-out Reset, a 2-wire
Serial Interface address match, an external level interrupt on INT0 or INT1, or a pin change
interrupt can wake up the MCU. This sleep mode basically halts all generated clocks, allowing
operation of asynchronous modules only.
INT0, INT1, and pin change interrupts will wake from any of the sleep modes.