For what you want, the GH2 is not the camera for you. At full resolution the fps does not compare to a real dslr.
For animal the E5 has the 2x crop so if your subject require allot of reach. The slightly smaller sensor will give you 600mm of reach with a 70-300mm lens in daylight.
The nikon and pentax with a 300mm lens will only give you 450mm or reach. And the E5 does focus faster then both the k-5 and d7000. And has a much longer burst rate then the nikon that will let you shot 6fps for about 2.5 sec only before slowing down to 1fps.
But the pentax and nikon are better low light camera. They are cleaner at 3200 and 6400iso then the E5.
The nikon will give you some really good lens options, but lenses with 600mm of reach will be expensive. The pentax k-x really do not have a very fast 300mm lens. The da 55-300mm is a sharp lens, but it does not focus as fast as the nikon and olympus lenses.
Super Frequent Flyer, no joke. Ex Patriot and loving it.
Canon Eos 60D, T1i/500D, Eos1, Eos 630, Olympus EPL-1, and a part time Pentax K-X shooter.