I hand calculated the instantaneous velocities for these cases using finite differences (central difference approximation), and, in neither case did I obtain a velocity variation with time anything like what loggerpro gave you. After the initial transient, the velocities were nearly constant (of course, with some expected scatter). For the first case, I got a terminal velocity of about 0.4 m/s, and, in the second case, about 0.25 m/s.
But neither of those tables match the distance-time graph linked at post #14 (which, in my view, does match the velocity-time graph and data originally posted). So I don't think these are from the right trial.