does a codec become more efficient when shooting b&w? with 4:2:0 or 4:1:1 it has 1/3 less incoming data to handle and with 4:2:2 it has 1/2 less data to handle.
It seems unlikely, because the recorded colour space and encoding is still exactly as before. The amount of incoming data would be the same.
In theory, eliminating differences in colour channel information aught to improve encoding efficiency, but I've no idea if the AVC encoder does this at the profile / implementation that the GH1 uses.
A more robust image in 8 bit territory is one that's closest to how it'll end up when finished.
Choose a picture profile that's near enough the right "look" out of the camera and needs minimal (or no) adjusting in post - especially if monochrome - as there's less variance in data to push and pull.
Either way, any improvement in encoder efficiency with a GH1 is not going to be significant. Its AVC encoder is somewhat poor (compared to a GH2) and super bit rate hacks won't work.
