actually I'm saying the lens is not good enough for the crop camera.that's a huge misconception. you don't get more reach, you get a cropped image, hence the name "crop camera". take any image you currently have and crop it, have you got more reach? no, you just have cropped it.I know when shooting with a crop camera, you get extra reach, which on Canon is 1.6x.
as @Helix_2648 already pointed, you get better ISO and dinamic range. how much? that depends on the cameras that you compare, but around 1 stop of improvement.