Since the GH2 is not compliant with the UHS-I standard (user manual), then surely the higher read/write speeds of the Extreme Pro cards would not be attainable in this camera. My understanding is that for non-compliant devices the card speed reverts to the Class 10 standard, i.e. minimum of 10 MB/sec. (from reading the release on the Transcend UHS-I Class 3).
A simple test on a hacked camera would answer your question but since it appears you haven't even tried , the answer is ....obviously yes . Normal class 10 cards don't cut it with higher bitrates, i.e. stop recording due to card error....and extreme pro cards continue recording. Sometimes I even get card error on medium bitrate mpeg720p with normal class 10.
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