Since the GH4 has a 2.34x crop in 4k mode, it seems like there would be some advantage to using the 45mm over the 60mm for macro shooting. The 45mm already acts like a 105mm on full frame, which is about as tight as you'd want to go. The 60mm, meanwhile, acts like a 140mm lens, which is much more limiting, I would think.
The other advantage the 45mm has is the O.I.S., which should come in handy with video.
Are there any benefits to using the Olympus 60mm for video?