Below what Vds voltage do NFETs get very low rdson?

Hello
We are delivering several kW's of power to a very low voltage system (1.8V). The downstream SMPS is obviously an array of paralleled sync Buck converters. Due to the obviously very low duty cycle of these sync Bucks, the sync FET is ON for the majority of the time. Therefore, the efficiency of the entire system is being determined by the rds(on) of the sync fets of these downstream sync bucks.

We therefore want to use as-low-as-possible rdson for these sync FETs……what do you think is the demarcation voltage, whereby there are very low rdson NFETs to be found in the market?
For example, we wish to set the vin to these sync bucks to be high enough to allow reduction of input current , but low enough to allow finding low enough rdson sync fets. Do you believe it is 20V?

I've seen 15V Mosfets.

Whether its RDSon is lower than a 20V Mosfet, an examination of the datasheets will tell.
But once you get below 10 milliohms, the soldering and layout techniques have as much, if not more, parasitic resistance.

thanks, actually it seems that 40v nfets are often found with just as low rdson as sub 20v nfets.