I have been shooting on a GH2 since it came out. That and a Nikon are the only digital cameras I've ever really used. Right away, I noticed that the sensor on this camera produces a pretty shitty and noisy image, compared to an APS-C Nikon. I'm not sure the specifics of why, but it seems like there is some information on the internet to corroborate the shittiness of the sensor. I am not referring to the in-camera jpeg, mind you, I'm referring to the raw data.

How much performance could I gain if I switched to a GH4 or a newer Olympus 4/3 camera? Or, am I better off switching to Canon, Nikon, or Sony?

(I am going back to film too, but that's a side project. I still need digital.)