a RAW comparison of the newest iteration of Olympus' sensor and Panny's new sensor, and the results are as close to identical as one could hope to get.
Obviously, there are subtle differences in the noise patterns, and the Oly appears to be achieving marginally better detail at low-ISO compliments of its complete lack of AA filter. If we're picking nits, and we may as well, the Olympus seems to be retaining color and fine detail slightly better by ISO 12,800. We'll have to wait and see whether the GH3's ISO rating are closer to nominal than the Oly, which was pretty far away, meaning that for every ISO rating, the Panny is slightly more sensitive.
Three-quarters through the page, they have a series of photos taken at ISO-200 and then over-exposed in Adobe. It shows a huge boost in dynamic range compared to the GH2. Impressive and much, much needed.