Re: 6V to 5v ~1mA max. typical 200uA. efficiency >90%
For high efficiency low power converters, charge pumps are pretty much the only option. But getting arbitrary conversion ratios can become very complicated. For example, converting between 5V and 3.3V isn't too difficult (there are chips that are designed to do this), but converting something like 6V to 5V is much more complicated, and would require many more switches and flying capacitors. And when the voltages change, either the ratios need to change (requiring more capacitors and switches, and a smart controller), or you have to accept decreased efficiency or output voltage error.
What are your ripple voltage requirements on the outputs?