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Yes, we call it SSQ or self selected Q Factor which you can measure using a special hanging task and some fancy 3D video equipment.
I built a set of sliding pedals to allow people to establish their own personal Q Factor and then this hanging task predicts what you end up with quite well. Unfortunately difficult to do without posh kit but something I've done for Pro Teams. Generally going for <142mm is a good idea for experienced riders.
Is the ideal Q-factor rider specific? Gains have been demonstrated below 140mm, but it's not clear if that was for one rider or an aggregate.
My guess is that ideally your legs should be in-line (ie ankles, knees & hips perpendicular to the horizontal), so it should be possible to measure your own Q-factor.