I've recently been taking a few street shots at night without flash using my Canon 20D with Canon 50/1.8 ll lens. This combination is extremely light. That 50/1.8 lens is razor sharp and as light as a feather. Unfortunately, it's not sharp at full aperture so I try to avoid shooting at f1.8. However, with camera set to ISO 1600 it's surprising how often one can get a full ETTR at f2.8 to f4, just with street lighting.
Because this set-up really is so light that one hardly notices a weight around one's neck, it occurred to me that an E-3 with Zuiko 12-60/2.8-4 would be so much more versatile because it's a zoom and has the benefit of IS.
It would be heavier of course, but the extra weight would be justified.
With this thought in mind, I set about finding comparisons on the net between the E-3 with 12-60 and a Canon 40D with equivalent lens. Although I have a 20D, I've already established that image quality in terms of noise and detail is very much on a par with the 40D which only appears to have the edge at a level of extreme pixel-peeping, represented by either huge prints or 200% enlargements on the monitor.
The results were surprising but not necessarily conclusive because one has to rely upon other people's testing methods and it's not always clear if the results may be skewed by differences in the jpeg output of the camera's being compared, or indeed if jpegs or RAW data were used.
The first comparisons I looked at were at Imaging-Resources where they have the identical still-life shot with both E-3 and 40D at all the ISO settings.
It's clear from these comparisons that the 40D has a noise advantage at high ISO. I'd estimate it as being 2/3rds to 1 stop. In other words, the 40D at ISO 3200 has very similar noise to the E-3 at ISO 1600, and 40D noise at ISO 1600 is very similar to E-3 noise at ISO 800. I'll be kind and give the E-3 a pixel-peeping edge, which is why I'd accept a 2/3rds stop noise advantage for the 40D instead of one full stop.
What this means is that for low light shooting at maximum aperture, the lens attached to the E3 needs to be at least 2/3rds of a stop faster to equal the low noise results from the 40D.
Is there such a lens? It appears not. The Zuiko 12-60/f2.8-4 seems to be all the rage at the moment, but it's not f2.8 across the whole FL range and it's not 2/3rds of a stop faster than the nearest Canon equivalent. Canon have an equivalent EF-S lens which is f2.8 across the whole range but has the disadvantage of not having as wide an FL range, only 17-55. If one considers the FL ratio between the 40D and the E-3 as being 1.25, then in E-3 terms the Canon 17-55 becomes a 13-44mm. I'd rather have 12-60mm, all else being equal.
Unfortunately, all else is not equal. I'm sure the Zuiko 12-60 is an excellent lens. However, from what I can find out on the net, so is the EF-S 17-55/2.8. At PhotoZone, test results show that this lens, in the centre, outperforms the Canon 50/1.8 prime at all apertures in common. At the edges it is only marginally less sharp than the 50/1.8 at the edges, using a cropped format camera such as the 350D.
Now, clearly for me it would make much more economic sense to buy an EFS 17-55/2.8 for my 20D, than buy into an E-3 system. Within the focal length range of the EF-S 17-55, results should be just as sharp (possibly sharper) and noise should be noticeably less at high ISO.
Just thought I'd pass on the results of my research. I don't mean to discourage anyone from buying into the E-3 system. There are lots of other areas where an E-3 system will outshine a 40D system; waterproof lenses, a greater choice of 3rd party lenses which don't need an in-built IS system etc.
However, in this particular comparison I've done, we're looking as a very similar price and weight for the respective packages, with the 40D outclassing (provisionally) the E-3 in terms of absolute image quality.