Stephen Schwartz says that, in the realm of Broadway musicals at least, false rhymes are regarded as poor craft--though it happens from time to time. I tend to agree--and bad scancion is death--

Cole Porter's lyrics seem to flow effortlessly--and it is because the scans are precise, the rhymes are perfect, and his words are elegently chosen--it is hard to misremember a Porter lyric, because no alternate wording works as well as the original--

As to the range question, a song isn't much good for a singalong if most people can't sing it--but it might work pretty well in an opera--