I really dug the image quality of the Olympus, however I honestly believe the Panasonic 12-35mm is just as good image quality wise. But of course at f2.8 it can't compare to the low light ability of the f1.8 of the Olympus. But the Panny can maintain f2.8 all the way through it's zoom. Constant-aperture. That's really nice.
Also, even though I don't use auto focus too much anymore, auto focus with the Olympus lens during video was dog ass slow on my G7. Where as with the 12-35mm lens it's pretty quick. Probably faster than the kit 14-42mm lens.
Before I bought the Panny 12-35mm I had considered a Metabones Speedbooster (MFT to Canon EF mount focal reducer) and Sigma 18-35mm f1.8. But that's like $1500. loooool However I might rent the Speedbooster and Sigma to check them out.
Yeah, with all that talk about lens swappability between Oly and Panny I bought into the hype and got the lens with the Leica optics. The image quality of the Panny 25 was considered tops from all the reviews I saw, but after looking at the images in Lightroom for the first time I was pissed because every single one of them suffered from both green/red and yellow/purple fringing everywhere, and it's so prevalent that it's not easily fixed. It wasn't until later I found out that the lenses are fine tuned for the bodies of their brand, and Olympus bodies lose out in this regard.
However, like you said, Oly lenses don't focus fast on Panny bodies. I've found that the 25 is pretty fast on my E-P5 however.
In short, before I spent money I wish someone would have just come out and said that it's better to match brands with bodies and lenses, it makes life easier.
P.S. - Unless you already have a bunch of appropriate glass, I'd steer clear of any speedboosters. The autofocus is still shit.
