Marc,

As the others have pointed out, you should go for the PD Mode for mainly two reasons:

1. Your MCU draws a lot of current, even in idle mode. You can expect that the power consumption during reset is somewhat between the idle and active mode, in PD Mode however, the oscillator is stopped and the MCU draws about 50uA !!!

2. Vcc can go down to 2V and still preserve IRAM contents.

Your design faces one tricky part: System RESET.
During cold power on, the MCU must have a reset applied until Vcc is steady above the minimum threshold - in your case 4.75V for reliable operation (some people like supervisory circuits release their reset 1V below that margin)
Now if you want to take advantage of the extended Vcc range in PD, you'll have to make sure that the MCU is reset AFTER the power is restored.

And another thing, while we're at it:
If you don't intend to power the external memories and the mighty latch (your circuit isn't really low power by design isn't it?), you should write zeros to all Ports that are connected to these devices, because the current that will flow through their clamping diode and powering the rest of your board will exceed their stand-by current.

Hope this gives some insights

Cheers, Roger