I've had my 12-40/2.8 now for just over a month, and I can honestly say that I have no desire to ever use the 12-50/3.5-6.3 again. Whatever aperture or focal length I choose, the results from that lens are simply subpar compared to the 12-40 - lots of CA, softness outside the center 1/3 of the frame and so on. The 12-40 is about the perfect size for the E-M5, balancing in my hands without any need for an external grip. The 12-40 has also convinced me that (non micro) 4/3 lenses are a dead-end. As much as I liked the optics of the 12-60/2.8-4.0 and 50-200/2.8-3.5 and others, fast competent autofocus is simply too much to give up. I've been getting shots that I hadn't been able to since I stopped using Nikon. Even the E-M1's PDAF solution with 4/3 lenses is nowhere near as fast and accurate as the AF on a good native lens. In short, the 12-40 has given my 16 month old E-M5 a new lease on life. I think Olympus made a real blunder not releasing this lens with that camera - by saddling the E-M5 with the 12-50 kit they dramatically undersold the capabilities of the E-M5 by pairing it with such a mediocre optic. A couple of samples from the 12-40.