I don't know if this has been posted before, but here's Mauri Galiano's very nice test which compares the GH4's various aspect ratios in 4k "Photo" mode using a Bolex 16/32 1.5x, an Isco 1.7x and a 2x Proskar.
This sealed my decision to finally pull the trigger on a GH4.
The only limitation I see right now is it's only in 30p and 25p. Apparently someone within Panasonic is pushing hard for 24p. Otherwise the GH4 (except low light) is an embarrsment of riches.
eris