The Panasonic oleds use the same LG wrgb oled panels in the end. So the gamut would majorly depend on that. The LG B7 does 99% of DCI-P3 so that should sort out most color volume questions in Rec.2020. For more coverage, oleds need to get brighter. Also there is no way the Panasonic can do better HDR as it only supports hdr10 with static metadata compared to the active(quasi dynamic) system for LG. On top of that it doesn't support Dolby Vision and Panasonic has no plans to support it either. The EOTF of the LG 2017 sets is biased towards preservation of shadow details with a much less aggressive ABL making it the best tv for HDR according to hdtvtest.co.uk whom I rate pretty highly for reviews of TVs.
The major benefit the Panasonic has over the LG for rec.709 content is a working cms. However almost all LGs seem to be well calibrated from factory so this is moot. For film mode or video mode interlaced content, the video processing on the Panasonic is far far superior. LG still has a long way to go to catch them. So if that is a major criteria, I would say get the Panasonic.
As far as I am concerned, I feel for 1080p or lower, it's better to use madvr with reclock on an htpc and upscaling to 4k60 with an nvidia gpu instead is a far better solution than using crappy sources and leaving the processing to the TV.