I think the big difference is going to be the size of the sensor... and it should have digic V v. digic 4 in the 60D. That should suggest that iso rating could be higher with less grain.
The Digic processor has nothing to do with the size of the sensor, or directly with the noise level of the sensor. They are separate components in the camera. The Digic can handle things like automatic white balance, autofocus, face detection, jpg encoding, noise reduction in jpg images, etc, while the sensor actually captures the light from the lens and converts it to electrical information. If you shoot RAW the noise/grain in the photo will be similar with a Digic 4 or Digic 5.
The next Rebel will almost certainly have the same size (APS-C) sensor as the 60D, T3i, T2i, 7D, etc, but it might have a newer version than the one currently found in those bodies. A newer sensor might do a better job at high ISOs or have a higher pixel count, among other things.
Last edited by m3m3; 05-11-2012 at 07:28 AM..