Its a bit like doing a road test comparison of a Ferrari vs. a Mini. They both go from A to B, the Mini's more practical in many situations, The Ferrari's probably more exhilerating (I've never driven one and probably never will).
BUT how may road testers would seriously do a comparison of the two side by side - I for one don't see the point.
The point, Paul, is to find out the strengths and weaknesses of each system, whether it be motor cars we're comparing or cameras. There might well be situations where the Mini Cooper (a souped up sports version of the original Morris Mini) will outperform the Ferrari, perhaps on a particularly tortuous circuit with sharp bends. I don't know, but I'm prepared to test the obvious.
The scientific method, it seems to me, is actually based upon the willingness and motivation of a few individuals in the past to test the obvious and discover something new. Things are not alway what they appear to be.
In this particular comparison I believe the original poster has not done justice to the G9. There are certain critical factors when taking a photo that are essential to get right for a technically good shot. This is not necessarilly a comprehensice list but such factors include; accurate focussing, correct exposure, sufficient shutter speed and desired DoF.
The G9 is limited with regard to choice of DoF. It's difficult to get a shallow DoF if that's what's desired, so in this respect the 1Ds is streets ahead. The 1Ds will also focus faster and more accurately, although I'm not sure if the greater accuracy is relevant to any comparison because the extensive DoF of G9 shots makes accurate focussing less critical. This is something which should be tested.
However, in situations where both extensive DoF is desired and a reasonably fast shutter speed to freeze either subject movement or camera shake when tripod is not available and lighting is poor, I would predict that the G9 will trounce the 1Ds regarding image quality; take it to the cleaners, so to speak.
In this situation I would expect the G9 not only to produce sharper images than the 1Ds with better color but much cleaner images by a very noticeable margin.
How come? Because the G9 at f2.8 produces the same DoF as the 1Ds at f13. To use the same shutter speed as the G9 at f2.8 and ISO 80, you'd need to bump up the ISO of the 1Ds to 2000. Oops! The 1Ds doesn't have an ISO 2000. Its maximum is 1250. Never mind! Canon has usually under-stated its ISO values. I'm not sure but I think ISO 1250 on the 1Ds is probably closer to ISO 2000, so lets compare the G9 at f2.8, ISO 80 and say 1/50th sec with the 1Ds at f13, ISO 1250 and 1/50th sec.
At ISO 1250 I think the IDS image will not look good. It'll be noisy and will have lost tonality and color saturation as well as dynamic range. It will also have lost resolution, not only due to excessive noise but also the inevitable slight softening of a lens at f13.
The above differences in DoF have been calculated by comparing the diagonal dimensions of the sensors; 9.5mm for the G9 and 43mm for the 1Ds. This ratio represents the difference in f stops for equivalent DoF, ie. 4.5 stops.