Mandelbaum vs. Ciardi as translators of Dante

I just finished Allen Mandelbaum's translation of the Inferno and found it much more moving that John Ciardi's, the only other translation I've read. As I did before with Goethe's Faust, I want to compare the two translations in terms of their accuracy by looking at a sample passage. I chose one of my favorite parts, Ulysses' speech to his shipmates (Canto XXVI, lines 112-120).

First, the original Italian:

    'O frati,' dissi, 'che per cento milia
perigli siete giunti a l'occidente,
a questa tanto picciola vigilia
    d'i nostri sensi ch'è del rimanente
non vogliate negar l'esperïenza
di retro al sol, del mondo sanza gente.
    Considerate la vostra semenza:
fatti non foste a viver come bruti,
ma per seguir virtute e canoscenza.'

Here's John Ciardi's rendition:

'Shipmates,' I said, 'who through a hundred thousand
    perils have reached the West, do not deny
    to the brief remaining watch our senses stand

experience of the world beyond the sun.
    Greeks! You were not born to live like brutes,
    but to press on toward manhood and recognition!'

And Allen Mandelbaum's:

    'Brothers,' I said, 'o you, who having crossed
a hundred thousand dangers, reach the west,
to this brief waking-time that still is left
    unto your senses, you must not deny
experience of that which lies beyond
the sun, and of the world that is unpeopled.
    Consider well the seed that gave you birth:
you were not made to live your lives as brutes,
but to be followers of worth and knowledge.'

Mandelbaum is clearly the more faithful to Dante here. Ciardi condense's Dante's nine lines into six, makes the first sentence hard to parse by throwing in the random word "stand" (to rhyme with "thousand," which it doesn't really), cuts out "the world that is unpeopled" altogether, and stretches his poetic license to the breaking point when he chooses to translate "Considerate la vostra semenza" as "Greeks!" (Mandelbaum's only real liberty -- adding "that gave you birth" -- seems a necessary one, since otherwise "your seed" would seem to be referring to descendants rather than ancestors.)

The two translators' very different renditions of "virtute e canoscenze" -- "manhood and recognition" vs. "worth and knowledge" -- are intriguing. Since my knowledge of Italian doesn't go much beyond the ability to recognize obvious cognates, and since both translations seem etymologically plausible, I don't know who's closer to the mark here. If I had to bet, though, I'd put my money on Mandelbaum. "Press on toward manhood" isn't the most natural exhortation to give to a company of veterans who are "already old and slow."