Are 生意気 ("namaiki", i.e. "cheeky") and メスガキ ("mesugaki") synonymous? I get the sense that the former is a component of the latter, but that doesn't apply the other way around.
Maybe current otaku parlance is such that "namaiki" (which is an adjective) refers to the character attribute whereas "mesugaki" (a noun) refers to the character embodying "namaiki"...