It’s nice to see some improvement in the low light abilities of the GH4, since this is one of the weaknesses of the GH4.
The Sony A7s series (I and II) are truly phenomenal in low light. However, light is a necessary ingredient to produce an excellent image and one should not use a camera with good light sensitivity as an excuse not to properly light their scene. If one has control over lighting we still prefer the image from the Panasonic GH4 over the Sony A7 series.
And since we are on the subject of the GH4, here’s a good video showing what the Varavon BirdyCam 3 axis gimbal stabilizer can do with a Panasonic GH4 attached to it (with the 12-35mm lens):