I had a great opprtunity to photograph a Barred Owl that was hanging around my yard for several hours (watching the bird feeders....though it mostly appeared sleepy....).
I took pictures with my Pana GH1 and 45-200 lens, and my Canon 50D with a 300 f/4 lens. These 2 pictures are quite close in time and settings, though not an absolute comparison. They were both shot in camera raw, an I did not process them. They are cropped to approx the same dimensions, though the focal lengths were a bit different.
The Canon was mounted on a tripod. The Panny was firmly balanced on top of the Canon, as I didn't feel I had time to remount. Panny was at a bit of a disadvantage, but with some post-processing, I think it could come out nearly as well as the Canon. The most obvious differences are different DOFs , color,and detail. Panny might have move ever so slightly. Wish I had a Panny 100-300 to compare....
Canon: 1/60 f5.6, iso 500 @300mm
Panny: 1/60 f/5.4, iso 400 @ 175mm