I have just spotted a delightful comment on this mishnah from Rabbi Eliezer Papo (a.k.a. the Pele Yo'etz), who was born in Sarajevo and served as rabbi in the Bulgarian town of Silistra during the Napoleonic era. He did not write a full-blown commentary on Pirkei Avot, but his thoughts on the tractate have been compiled on a chapter-by-chapter basis and inserted within the body of the second volume of his Torah commentary Eleph HaMagen.
Much of the Eleph HaMagen is either kabbalistic or somewhat off-the-wall in comparison with the sort of Torah writing that occupies the mainstream of contemporary Torah literature. This comment on Avot 5:23 is however refreshingly accessible. It runs like this:Many times the Torah is compared to great wealth, for example Proverbs 2:4 ("If you seek [the Torah] like silver, and search for it like hidden treasure..."). However, any comparison of the Torah with gold, silver or other material wealth faces four problems. The Pele Yo'etz lists them together with their solutions::
1. There are things that a person wouldn't even do for money because they'd be too embarrassed (e.g. being offered a large sum to go around naked in public). The leopard however is brazen and feels no shame or embarrassment. This is essential when learning Torah, if there are questions to be asked that some may consider downright stupid;
2. A person may not want more money than others have, for the commendable reason that he is perfectly content with what he has. The eagle however aspires to soar above competing birds. This continuing aspiration to rise is a great motivating factor;3. Running after money creates a poor impression. People usually prefer to seek it more discreetly, at a leisurely pace. The deer runs but, wherever it does so, it never forgets to run back to its home. The talmid's thoughts may run in many directions, but should always run back to the makom, the place, which is their source: the Torah;
4. When a person has material wealth, it is easy to become afraid of losing it and thus be preoccupied with ways and means of keeping it safe. Lions, being strong, are not afraid, particular when it comes to performing mitzvot.
This may not have been quite what the author of the mishnah had in mind, but it scores high in terms of relevance.