Compared to Pana100-300

From my perspective, here the main advantages of the Zuiko 75-300:
-20% Lighter and smaller volume with a minimum open aperture disadvantage (in practice less than half an aperture)
-deutlich higher Trefferqute the C-AF (Continuous AF)
-after all published tests and in contrary of the Pana 100-300mm no drop in resolution (also centered) from about 200 / 250mm - even with my copy not
-low stray light susceptibility
-Fits with the E-M5 and rubber diaphragm in the StreetCaseL +2 smaller lenses

It makes sense can be used in the Olympus E-M5, the lens due to the anti-roll bars and the High ISO capability.