Obviously, there is a slight power and velocity difference between 1.06J and 1.09J; however, it should not really be noticeable. Are the barrels the same length or is one significantly longer than the other? The 0.24J power change is pretty hard to explain unless you have gone from a short, wide bore barrel to a long, tighter bore barrel.
A weaker spring and a tighter barrel is usually better as it puts less stress on the gearbox, unless the combination of a weak spring and a fast motor/gear set leads to overspin, which can be cured with an AB mosfet anyway.