Rob,
It would be interesting to compare an Oly 4/3rds body with 12-60mm lens and the Canon 40D with 17-55mm lens.
The Zuiko lens has the obvious advantage of a slightly wider range and the 17-55 has the advantage of being 1 stop faster at all focal lengths.
Checking out my current problems with autofocus accuracy of the 17-55, I find that this zoom is virtually as sharp at F2.8 as my Canon 50/1.8 II prime at F2.8.
At F2.8, the prime is 2 stops down. The zoom is at maximum aperture, so this is an impressive result. Edge resolution is also very similar despite the fact that the 50mm prime is designed for a larger format. Don't be fooled by the slightly different lighting conditions between the shots below. However, in this extreme pixel peeping situation at 200% enlargement, the Canon 50/1.8 prime has the edge by a very small margin of complete insignificance even in a large print.
When I buy a new camera, I want some clear and definite improvement that matters, whether it's resolution, autofocus capability, lower noise, higher ISO performance or faster frame rate.
The 40D has a faster frame rate and the manual focussing facility of LiveView. I intended to buy the 17-55/2.8 IS for use with my 20D, but ended up buying a 40D body as well because the price was so good.
But the only reason I even considered such a purchase was as a result of a very pleasant experience walking around with a 20D and 50/1.8 prime at night in Chiang Mai taking shots without flash. Flash seems to me to have a very harsh effect on photos at night, outdoors. You can't bounce the flash off a white ceiling, you get unwanted shadows like the shadow of a nose against a cheek, an inky black far background and a noisy near background. If it's possible to refrain from using flash, I'd prefer it.
The 17-55/2.8 IS on the 40D increase the options of being able to do this. When I recently attended a Chinese New Year dinner, I brought along my 40D and 17-55 zoom to take the obligatory snapshots. The first shots I used flash, then discovered flash wasn't necessary. ISO 3200 at F2.8 or even F4 allowed for a shutter speed plenty fast enough. I much prefer the shots without flash.
I think anyone with an E-3 and 12-60/F4 would be struggling to get good shots in these circumstances, just as they would walking around at night in Chinag Mai or any large city, simply because the 12-60 is a stop slower and the E-3 is a stop noisier at high ISO. That's 2 stops difference. Quite significant.
On the other hand, if Canon can not get my 17-55 to autofocus accurately and, if the 12-60 is simply a sharper lens, system-wise, bearing in mind that it needs to be sharper because of the slightly smaller sensor of the E-3, then such advantages of the 40D/17-55 would be offset.
The following shots were focussed at or near infinity. The precise focus point was the landscaped wall immediately below the car. From left to right:
(1) The over all scene.
(2) Manual versus autofocus of the 17-55 at 51mm.
(3) The 50/1.8 prime at F2.8, auto focus, versus the 17-55 at 51mm and F2.8, manual focus.
(4) Left side edge comparison between the 2 lenses.
[attachment=5384:attachment] [attachment=5385:attachment] [attachment=5386:attachment] [attachment=5387:attachment]