I did a quick test today comparing the three cameras. It's a cloudy dull day sadly, but I gave it a go anyway. I set all the cameras on AWB, 200 ISO, F9 on the AV setting at 70mm on a tripod...letting the camera do the rest. I zoomed in to 100% on each image and cropped 800 x 600 pixels. Because of the different sensor sizes the images won't be exactly the same. I have done no post processing to any of the images, these crops are from the raw images.
First up the Olympus E3 with the 50-200mm 2.8-3.5 lens set at 70mm. (note: properties says 72mm)
Next is the Canon 30D with the 28-135mm 3.5-5.6 IS lens at 70mm:
Last is the Canon 5D II with 24-70mm 2.8 L lens at 70mm:
In hindsight I probably should have done the maths and shot these all at the same focal length. Might do next time, but I did want to see the difference the different size sensors had as well.
First thing I noticed is that there is a big difference in size with the E3, as expected with a 4/3rds sensor. Next thing I noticed is that the clarity with the 5D II and 24-70 lens was much clearer and quite a bit more detail than the others.
More test to come.