But this was too much fun to delete -- paricularly in the middle of said beastly month.

Quite agree - G&S are always worth quoting, even if they not at all pertinent. And this quote points up what looks like a change in pronunciation between C19 and now. "This beastly month" appears to have been spoken as a four syllable word to rhyme with "fairy", whereas now, in UK at least, February is contracted to three syllables and slurred to "Febr'ry" (indeed, often enough cut down to a 2 syllable "Febry")
Was Gilbert exagerating the word, does anyone know, for lyrical/poetic purposes, or did the Victorians - well, the posh ones - pronounce the word as he uses it?