Congrats to Jim Kasson (often contributes here) who finally has his GFX-100, hurrah.
His blog provides many technically details insights
hereIncluding:
the dual gain bump is at 500iso, not 640 or 800.
the sensor is GBRG array rather than the classic RGGB
the Phase Detect AF pixels are positioned 18 pixels apart over Red positions.
very little LoCA shift, at least with the 110mm/f2 lens.
Some of his posts are of detailed technical interest, others, like recognising the 500asa gain bump, are relevant to regular use of the camera. Maybe Jim himself can emphasize any essential details, but my thanks for his research.