Gaudeamus has been and is used as the Introit for the Mass on many saints' days, beginning, apparently, with St. Agatha's. It's now associated in the Proper of Saints with both All Saints' Day and the Feast of the Assumption. Here's the chant score, with the words used for the latter feast:
Here are the words used for the Feast of St. Benedict, in Latin (including the Psalm verse), along with an English translation:
Gaudeamus omnes in Domino diem festum celebrantes
sub honore Benedicti abatis de cujus solemnitate gaudent
angeli et collaudant Filium Dei.
Magnus Dominus et laudabilis nimis
In civitate Dei nostri in monte sancto ejus.
Gloria Patri et Filio et Spiritui Sancto
Sicut erat in principio et nunc et semper et in saecula saeculorum. Amen.
Let us all rejoice in the Lord, celebrating the feast
in honor of Benedict, in whose happy solemnity
The angels rejoice and praise the Son of God.
Great is the Lord and greatly to be praised
In the city of our God, on his holy mountain.
Glory to the Father and to the Son and to the Holy Spirit
As it was in the beginning, is now, and ever shall be, world without end. Amen.)
More about Gaudeamus, from the chapter "Josquin's Mass for All Saints and the Book of Revelation" in a book titled Symbolic scores: Studies in the music of the Renaissance:
It should be pointed out, however, that the Introit "Gaudeamus" - as ascertained already by Helmuth Ostoff - is also used for a large number of saints' days as well as for the feast of All Saints (November 1). The Introit sung in the Mass of Saint Agatha (February 5) is the oldest version. Its text is the same as that of Example 1, except that it has "Agathae martyres: de cujus passione" (Agatha martyr, at whose passion) instead of "Mariae virginis: de cujus assumptionae" (the Virgin Mary, for whose Assumption). From the eleventh century onwards, the antiphon appears in at least seven other Masses. In the Introit of All Saints the text passage quoted above reads "Sanctorum omnium de quorum solemnitate" (of all the Saints, at whose solemnity).
The YouTube page for the above video notes that the singers are the "Monastic Choir of the Abbey of Notre Dame de Fontgombault."
And the following comes from the website of the Clear Creek Monastery in Oklahoma; they seem to be offering this recording. Not surprising, since they are Benedictines and all the music here (including the above Introit, which comes from this CD) is dedicated to St. Benedict. Note the different feast dates!
No one should be surprised to hear an antiphon in praise of Saint Joseph at the end of this recording: for the monks of Fontgombault offer this disc to him whom they loved as Joseph Cardinal Ratzinger, before receiving and venerating him as their Holy Father, Pope Benedict XVI.
1. Introit (July 11th): Gaudeamus The Life of Saint Benedict
2. Introit (December 4th): Vir Dei Benedictus
3. Antiphons (July 11th): Fuit vir - Beatus vir Benedictus - Glorious - Erat vir Domini Benedictus - Vir Domini Benedictus
4. Hymn (Matins, March 21st): Quidquid antiqui
5. Antiphons (feast of St. Scholastica): Egredere modo frater - Parcat tibi soror -Ecce te rogavi - Loquamur nunc - Cum Sanctus Benedictus
6. Communion (July 11th): Fidelis servus The Death of Saint Benedict
7. Sequence (July 11th): Læta dies
8. Antiphon of Magnificat (11th Vespers of March 21st): Hodie
9. Ant. of Magnificat (11th Vespers of March 21st): Sanctus Benedictus The Translation of the Relics of Saint Benedict
10. Ant. of Magnificat (1st Vespers of July 11th): Galliarum populis
11. Prolix responsory (1st Vespers of July 11th): Obviam
12. Antiphon of Benedictus (Lauds July 11th): Exsultaverunt
13. Hymn (Vespers July 11th): Claris Conjubila
14. Antiphon of Magnificat (11th Vespers of July 11th): Hodie The Glory of Saint Benedict
15. Gradual (July 11th): Domine præventisi
16. Hymn (Lauds July 11th): Inter æternas
17. Offertory (July 11th): Desiderium
18. Antiphon of Magnificat (1st Vespers of March 21st): Exsultet omnium Prayer to Saint Benedict
19. Alleluia (July 11th): Vir Dei Benedictus
20. Antiphon of Benedictus (Lauds March 21st): Sanctissime
21. Short Responsory (March 21st): Sancte Pater Benedicte
22. Prolix Responsory (1st Vespers of March 21st): Sanctissime
23. Antiphon of Magnificat (11th Vespers of December 4th): O Cælestis norma vitæ In Homage to Pope Benedict XVI 24. Antiphon (to Saint Joseph): O felicem virum -- Ps. Exaudiat
Several of the selections are available for listening at that page. And here's a post for about Office hymns for this feast day.
(A florilegium is a compilation; literally, the word means "a gathering of flowers.")