I bought the 12-60mm lens as a kit with the E-3 and had the opportunity to test it on vacation in Tuscany, since I already following lenses: 14-42mm, 14-54mm, 40-150mm, 70-300mm , have 50mm, I can only say that the speed, the imaging performance at 12-60mm are fantastic. Even with 12mm the distortion is still quite low. I've tested it also on the E-510 and it is there much better than the 14-54mm. From me a clear Best Buy!
