I can't quote Daniel's message--my browser won't show the formatting tools, etc.
I corrected my error in my second message. The crop factor is close, though one has to figure out which way to apply it, as I showed. It all depends upon what you want to be the same: framing, perspective, or both. You only have three variables: distance, focal length, and aperture.
Applying it to point-and-shoot cameras in another example, using the Canon S3 IS (6x FOVCF).
S3, 16.7mm (equivalent to 100mm full-frame), 50 ft, f/2.8: 28.1 - 228.6 ft, total 200.5 ft, 21.9 ft in front, 178.6 ft behind
That would have the same perspective and framing as my last 5D example:
5D, 100mm, 50 ft, f/2.8: 44.3 - 57.4 ft, total 13.1 ft, 5.7 ft in front, 7.4 ft behind
Now, stop down the 5D to 6 x 2 = f/16.8. DOFMaster only has f/16, at 29 - 183 ft, and f/18, 27.5 - 273 ft, so f/16.8 would probably be about right.
I can't argue with your analysis, Daniel--I certainly don't know enough to argue, except for one thing: for me, shutter speed, itself, is important--not for "camera shake," but for moving subjects. In that case, the light per unit area per unit time does matter. If all you photograph are static scenes, you're probably right, though I expect that there's some effect of the size of the "pixels." (The 1.6x bodies generally use smaller pixels, especially the high-density bodies like the 50D.) However, photograph a galloping horse with a 5x7 view camera. For the same perspective (distance) and framing, you'll need the same shutter speed as a full-frame, 1.6x body or 6x point-and-shoot to stop the action. What counts there is the angular speed of the moving parts, which translates into motion blur. Theoretically, it wouldn't depend upon focal length/framing, but only upon distance. However, in practical terms, a shorter focal length lens gives a smaller image of the horse, so the motion blur isn't as noticeable. As I recall, that's also the reason for the 1/FL guideline, essentially the angular rate as a fraction of the field of view, though correct me if I'm wrong. (It won't be the first time.)