Peety3 can correct me if I am wrong, but I think that his comment was based on available lens/body combinations. EFS lenses will work on the 1.6x cropped sensor bodies such as the 7D but not the 1D3, which is a 1.3x cropped sensor body. So, with the EFS 15-85 you can have a FF equivalent of 24 mm on a 1.6x cropped sensor body. However, you have to use EF lenses on the 1D3, thus if you were to mount the EF 24-105 on the 1D3, you'd have the FF equivalent of 31 mm. Of course, you could counter with the EF 16-35 for the 1D3 but countering with the EFS 10-22 on a 1.6x cropped sensor body would still be wider.
So, at each step, because EFS lenses work on APS-C bodies but not APS-H bodies, the APS-C can actually shoot wider than APS-H by using EFS lenses.
Weird, slightly counterintuitive, but true.
EDIT---John beat me too it....![]()
I'd say comparable to ISO 1600, but noise and the quality of the noise is better on the 1D3 at 1600 and beyond.
Here's a tilt-shift shot on the 7D that I think was at ISO 3200. Very unimpressed with the noisiness: http://www.flickr.com/photos/alibear...57632860559787
Both cameras can produce stunning images, the 7D will (usually) require better light to do so. They are slightly different tools but with proper use you will not have any IQ problem with either one. They are a little behind in terms of technology but they both still can produce great pictures.
PS: Look up a guy named Daniel Cadieux.......nature photographer who uses a 7D....I think you'll be impressed.