Seems like I've read AVC something cropping up a lot here. I'm shooting only 4k on GH4 and it has a few options, just not sure what fits vegas best. tried some tests but couldn't see big differences. BUT I didn't try editing a full 30 min time line of it, just little tests. Thanks!
I believe the GH4 files are ok in Vegas and if your machine doesn't do to well with it there is always the option of proxies. I use Vegasaur for proxies as it has more options than the build in proxy builder.
I usually shoot UHD 29.97p AVC+PCM MP4 files on my GH4 and they work fine in VP13/14/15, even without GPU acceleration. I often use Preview (full) playback, which looks almost the same as Best (full) on my 1920x1200 display to me, and can give a little smoothness advantage if I have multiple FX on.
I also shoot 24p C4K sometimes and that's fine too.
It shouldn't matter if you shoot MP4 or MOV. They're both decoded in Vegas by the same codec.