I have not - but I generally run 80-90 psi on my 25 tubeless - if I ever have a bunch I time it would a cool experiment to test different pressures, but my gut is telling me that it would not be very much difference until the pressure was lower than 50 - and you probably would not want to ride on normal roads with that. Yes, and I am sure if you dig enough you will find testing by pro teams and manufac. that would should the different rolling resistance of different psi.
