Comparison photos: made with either a Panasonic Lumix 45 - 200mm f5.6 m43 lens or Olympus 40-150mm f2.8 m43 lens with 1.4 tele-extender; not a fair comparison, due to the cost difference between the two lenses.
The Lumix lens still is a very good lens for birds and wildlife; more compact and lighter and saw me through my experimentation with micro 4/3 cameras.
However, over the short amount of time I've been using the Olympus 40-150 f2.8 PRO lens, I think it is superb! No image degradation with the 1.4x tele-extender that I can tell visually. It is matched very well with the Olympus OM-D EM-5 body.
The very small American Toad was photographed at my home.
All images have been cropped.