hi
they do shoot with less recoil and alot sweeter to as there is less volume, so you dont need such a strong spring to get them in the 11-11.5 ft/lb power range, lock time is also reduced, this is why you hear alot of people short stroking there spring rifles because they shoot that much sweeter!
the reason hw introduced the 26mm piston was there was a demand for higher power (FAC) and the 25mm pistons dident have the swept volume to output higher levels of power.
hope that made some sence sounded ok in my head.
Taito