I have to agree with FF, sub-12 ft/lb air rifles don't kill by dumping energy into the quarry - there's so little of it to begin with. They kill by destroying vital tissue. A pellet that passes through a creature's brain will actually cause more trauma than one that stops short.
Wadcutters, such as Hobby, can be devastating against fur - the flat face causes more trauma - but aren't so hot against feather, as they tend to featherball quite badly, which retards penetration and can prevent the pellet reaching the heart on a body shot...