another advantage the E3 system seems to have is sharpness at the corners. my 5d would be less sharp at the edges with all but the best glass. with the e3 and zuiko lenses the sharpness seems uniform from center to edge. this is of course due to the fact the the sensor is half the size. also i have noticed that the wide angle lenses from olympus seem to be better then the wide angle lenses i had with the 5d. again this is from my experience.
Once again, you have to provide more information here. All lenses, almost without exception, suffer from some degree of vignetting and resolution fall-off in the extreme corners and edges. The advantage of the Canon cropped formats is this fall-off is much less when using lenses designed for the bigger format, ie 35mm lenses, but is still a problem when using EF-S lenses.
The E-3 and FF 35mm are both similar in the sense that they use lenses specifically designed for the format.
However, it might well be the case that some Zuiko lenses suffer less from this problem. It might even be the case that all
Zuiko lenses suffer less from this problem compared with their 35mm equivalents. I would like to see some comparisons.
If you do show some comparisons, you should use the apertures which you would normally use with each camera. For example, when you want a fairly shallow DoF for portraiture, you would probably use f2 with the E-3. Whereas, with the 5D you would use F4 for the same artistic effect. On the other hand, for a landscape you might choose f5.6 with a Zuiko lens, which is probably the aperture at which the lens is sharpest and which would give you a DoF equivalent to the 5D at F11.
Now without seeing the test results I'm going to predict what the results might be, if you were to shoot the above examples.
The portrait shot at f2 would probably not be as sharp as the 5D shot at f4 because lenses usually aren't their sharpest at full aperture. Likewise, vignetting is generally worse at full aperture. If the 5D lens has been stopped down to reach F4 and it's a good lens, it will likely have less vignetting and will be considerably sharper in the corners. On the other hand, when shallow DoF is sought, usually the corners don't matter. But the 5D image should have slightly more... je ne sais quoi.... 3D effect .
Comparing the landscape shots, the 35mm lens is beginning to be limited by diffraction at F11, but at F11 vignetting should not be noticeable unless it's a very wide angle lens. One might expect the E-3 shot to have an appearance of slightly greater accutance despite having slightly fewer pixels. Whether or not the 5D shot could be sharpened appropriately to get the same effect would be interesting to find out.