Just a few wide open test shots of E-M5 + 75-300mm f4.8/6.7 at various focal length under weak evening light. I also happen to have a panasonic GH2 + 100-300mm combo which my wife uses for casual birding, I must say the Oly 75-300mm is noticeably sharper wide open on E-M5 then the Panny 100-300mm. Oly's f/6.7 at 300mm may be slightly slower then Panny's f/5.6, but not a problem on an E-M5 as E-M5 is capable of handling high iso and will be able to make up for the lost speed by shooting at slightly higher iso. If you are considering long range MFT lens for your E-M5, do try out Oly 75-300mm. I almost always shoot wide open with this lens.
iso1600, 300mm, f6.7, 1/250s, handheld
iso1000, 300mm, f6.7, 1/250s, handheld
iso250, 100mm, f5.1, 1/200s, handheld
iso800, 75mm, f4.8, 1/160s, handheld