For starters you could always measure the power consumption that the Pi pulls from the USB power supply. As long as you don't change many variables when compari

For starters you could always measure the power consumption that the Pi pulls from the USB power supply. As long as you don't change many variables when comparing software (like plugging in additional peripherals) it should be a decent way to get an idea of the power draw of the whole system under different circumstances. Or just measure the CPU usage and naively assume that lower CPU usage always means lower power draw.