Both done in the drops at relative steady state. Wind conditions were actually worse on the second example. Exact same power meter with exact same offset value.
Old bike (Niner BSB) with gravel wheels, 32c slick tires, a dirty drivetrain, and bottom bracket with old bearings
New bike (Tarmac SL6) with Roval CL50, 26c tires, clean drivetrain
I was surprised that the difference was so large.