Tips for Hero6 240 fps H.265 footage editing

Hi All

New to Premiere pro, not to video editing.  Just got the Hero 6 and shot a snowboard trip in all 1080 120 and 240 fps, which encodes in H.264 and H.265 respectively.  The 120 fps footage scrubs and plays smoothly enough, the 240 fps stuff really struggles on my machine.  I was learning about and trying to investigate using a proxy to help the playback, generated one but it creates a 60fps file that effectively plays at 4x speed, with normal audio speed.  It just holds the last frame for the end duration of the clip.  I also was investigating creating a encoder preset to ingest the files at a lower frame rate for the content that I don't want at full slow mo, but I can't find an option to H.264 at 120 fps, to effectively cut the H.265 240 fps down to a more manageable file.  All I see is 60 fps for the max framerate to encode H.264, and 120 fps to encode H.265.  I don't actually see any options for H.265 240 fps, only 300 fps which is weird.

So I think I just need to struggle through the areas that I actually want 240 fps available for smooth slow mo and then encode/ingest anything else to a more manageable format?

Any insight would be appreciated.

Thanks!