If the spring return faster, that'd mean it's exerting more force.
There is also the possibility that the spring is closer to a perfect spring than the standard silver ones.
and ^^ that is being perceived as "more springy" or returning "faster". So the acceleration is constant, whereas a less perfect "silver spring" would not accelerate evenly as it relaxed..
THIS IS SPECULATION... I highly doubt humans can perceive such a difference in 4mm travel.
