Not many a7s vs gh4 tests so far, but It looks like much more are comming next days.
The first interesting - dynamic range:
http://***URL not allowed***/dynamic-range-sony-a7s-vs-arri-amira-canon-c300-5d-mark-iii-1dc-panasonic-gh4/
Not sure If I agree with their methodology, but pure pictures speak for themselves:
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