Roger Cicala at lensrentals.com has been running quite a few lens tests lately (he also did one for NEX lenses which I didn't comment on because I hadn't finished my own testing yet). His results with the m4/3 wides basically mimic what I see in my tests (with the GH2 and OM-D as the test cameras).
Take a look at his lens test results here, then come back for a couple of my own comments.
First, I'm not sure why he says he was disappointed in the Panasonic 7-14mm. Compare it against its primary competitor, the Olympus 9-18mm. There's a clear, measurable difference between the two. In my experience you only pick the Olympus if absolute compactness is important to you. Indeed, the 7-14mm does reasonably well against the primes even when the primes are stopped down and the zoom is still at full aperture (though as you'd expect, it doesn't match, let alone top them). That's the price you pay for using a complex zoom, typically. But I have to say that the Panasonic 7-14mm is clearly one of the better zooms available for the m4/3 system. I'm never disappointed in my results with it. Given that it's a wide angle zoom in a small format, that's saying a lot. (The smaller the format, the better the lens designs have to be in order to perform well.)
It didn't surprise me that the Olympus 12mm and Panasonic 14mm and 20mm performed quite well in his tests, especially stopping down to get away from max aperture issues. Those three lenses are small enough to be in my "always carry" set, and I've never been disappointed in their performance. (See Thom's m4/3 Bag for what I usually carry.)
I was a little surprised at his 12-50mm versus 14-42mm results. Perhaps we have some sample variation to deal with here, as my 12-50mm doesn't outperform my 14-42mm by as much as Roger found with his copies (that's not to say that my 12-50mm doesn't outperform my 14-42mm, just not by as much as indicated in Roger's tests). I'll have to see if I can scrounge up some additional samples before I finish my reviews of those lenses. But I'm struck here, too, by the "compact lens doesn't quite match the larger lens" results.
What's missing in Roger's tests are the Panasonic kit zooms, both the original 14-45mm and the X version. Here, too, I suspect sample variation, as I've had two of the original, one of which was very good (better than the Olympus) and the other of which was less good.
Finally, Roger's comment about the Olympus 17mm bears noting: Olympus really needs to redesign this lens. It's the clear under performer in the wide offerings, basically only matching the kit zoom at the equivalent settings. Given that it's only a half stop faster than the collapsing kit lens, there isn't much to make one decide to purchase it.
One final point. I'm not sure how Roger tested, but I found that on a couple of the lenses hoods made a measurable difference (there's a fair amount of ambient light in my test rig, which is done to approximate what you encounter in real use). Too bad Olympus makes you buy hoods even on the expensive lenses (12mm f/2, for example). Likewise, finding appropriate hoods for some of the compacts isn't always easy, either.
