Mega Pro 3v3 serial ports

Hi All,

Designed a few arduino based low power data loggers over the last 3 years.

Thinking about purchasing a Mega Pro 3v3 for another low power data logger project.

Curious if anybody has tested using all 4 serial ports at the same time?

what is the highest baud rate that could be used?

Basically wondering if the move from 16MHz → 8MHz has any effect on operating 4 serial ports.

I understand that we are polling each sequentially with serial.available()

Also curious if anybody has any power consumption figures for when it is put in SLEEP_MODE_PWR_DOWN?

watch dog and brownout are disable in my current systems.

Jeff