I've just finished a project using the same camera and video specs and the playback was somehow sluggish, I've ended up using proxies to be able to work comfortably. My computer specs are a little bit low: i7-5930, geforce1080 ti, 64 Gb ram, win 10. Another thing: I noticed that PPro doesn't use hardware decoding when playing back those videos (needs support for that codec from Adobe?)
Sorry for the frustration on performance. I have noted that most people having performance issues are running H.264/HEVC 10 bit 4:2:2 variants. For now, I'll recommend using proxies or transcoding the original files. Please let the devs know you'd like this improved over on User Voice.