Apple displays are too expensive. Dell have some nice high resolution monitors (not 4K). But I heard that some graphics professionals prefer NEC monitors. Those are expensive as well.
Here are some shots with the Tiffen VND filter with G X Vario 12-35mm at f/3.2 ss 60 on the GH4 except the last shot which is without filter and in slow motion at 96fps. So you can see how the GH4 slow motion. It's indeed a bit soft.