The name of the game is penetration depth not speed.
Nickel plated shot penetrates further than lead and copper plated shot.
Yes, prairie storm shells contain 30% nickel plated shot.
On top of that testing done did find that 1500 fps loads produced a lower pattern percentage in a 30″ circle at 30 and 40 yards compared to lower velocity loads (1220 and 1350 fps).
1 1/4oz #5 and 1220 fps is still the overall winner in terms of pattern percentage vs penetration power for pheasants. This is for 12 ga. of course.