Here are some shots at 100-800 ISO from both the 1Ds Mark III and the 7D. Studio, and to get to the next step, I just changed both ISO and Aperture up in both cases each time.
The shots below are a crop detail from this setup, lit with one umbrella and one softbox fired with pocketwizards. I used a 35mm prime lens on the 7D, and a 50mm prime on the 1Ds MkIII, in order to get the same field of view.
Important – click on each image to see a pixel-for-pixel real-size preview.
So here we start at 100 ISO:
Now take a look at 200 ISO:
Now up to 400 ISO:
And finally, 800 ISO. Now we start to see noise, but keep in mind, these are real-sized crops. In reality, even at 8″x10″ you would see little.