Here's the numbers for energy...
For 7/8-oz loads, 20-ga Remington Managed Recoil target loads have an advertised velocity of 1100 fps, Premiere target loads are at 1200 fps and the Managed Recoil slugs are at 1290 fps.
Energy varies with the square of the velocity. So, increasing from 1100 to 1290 fps represents an energy increase of 37.5% That seems significant to me.
1290^2 = 1664100
1100^2 = 1210000