I can see why someone might choose G4 (aka Grade 43) over G3 (aka Grade 30), but it seems a bit extreme to say that G3 is not ideal (I realize it sounds like someone said it to you). For example, everyone might not be looking for the "less weight" of G4 (for same strength). For another example, someone might have a gipsy already sized for G3 proof coil -- then it seems as though it *would* be ideal.

BBB is a different link shape than proof coil, but it is also G3 "grade" metal. BBB is shorter links, supposedly to coil down into the locker better (without kinking, etc.). I don't say "supposedly" because I doubt it, but only because I have not tested the two side-by-side on the same boat.

You can find the exact link measurements of different chain sizes on industry sites such as Peerless/Acco's.