i suppose it would be possible with two frames, indoors, same weather, same rider, same wheels and tires and cassette, same chain, brand new matching cranks, add some weights to match up frame weights, same power pedals, ride at a predetermined cadence and power and carefully measure speed of the bicycle.

it would be pretty surprising if the difference between a noodly frame and a worlds-stiffest would be measurable, or above the margin of error of the experiment. but it would probably feel totally different to the rider, which is what’s actually important for most of us.