There is no silly question, just be more accurate please. If you are familiar with stuffs what is this headache with the drain-source voltage? In general a simple diode-connected device force the transitor to operate in saturation, 65nm shouldn't matter, and this is probably not a useful information for you.
It would be better to discuss about your unique case, where you have an issue, which transistor not saturates, show a schematic with annotated voltages for example with the headache.
And choice of device sizes is a complex question, depends on what you want, what is available. For example you obviously don't want big area with big costs, but some is required, because you have a minimal width+length too, and maybe even more area is necessary for matching, for load drive capability, or for noise reduction, but you want much smaller area to reach the target, then you have to find other circuit structure and/or you have to reduce an other parameter, like bandwidth, or you have to increase the consumption....for example. It is too complicated, references give a basic explaination for more parameters separately, but because these are multivariable systems noone can or wants to give an ultimate solution. That simply wouldn't work. And You, the designer has to give the specifications.