mmcp42:
as far as I can tell the only difference is support for pico power and brown out detection
the P-PU does, the -PU doesn't
Both have the BOD, but it can only be disabled on the 328P. But if ultra-low-power sleep modes aren't a requirement, then macht nichts.
I'm not sure the datasheet gets it completely right, Tables 29-8 and 29-9 show the same power-down current, 0.1µA typical, yet the BOD will draw ~22µA at 5V and 25C. Similarly, the charts in sections 30.7.4 and 30.8.4 look suspiciously alike.