Feast of BVM visiting Elizabeth

The reading of 1 Peter was interrupted by 2 feasts. Today, we celebrate the Feast of the BVM visiting Elizabeth. The story was recorded in Luke 1:39-56 where we find the beautiful Magnificat. The readings today include Romans 12:9-16. The church in Rome was already established and Paul wrote this epistle before he visited them. The church in Rome composed of Jewish and Gentile Christians. In the reading today, we find 2 quotations of the OT. Out of curiosity, I would like to see if Paul made use of the Septuagint.
The epistle to the Romans can roughly be divided into 2 parts. The first 11 chapters deal with theological questions and the rest ethical. So, the reading today deals with how Christians should lead their life. For example,
Let love be genuine; hate what is evil, hold fast to what is good (Romans 12:9).
Bless those who persecute you; bless and do not curse them (Romans 12:14).
Repay no one evil for evil, but take thought for what is noble in the sight of all (Romans 12:17).
These are high moral grounds on which Christians should stand firm.
Suffer patiently for injustice. Let God handles it.
Beloved, never avenge yourselves, but leave it to the wrath of God; for it is written, "Vengeance is mine, I will repay, says the Lord." (Romans 12:19)
Here comes the first OT quotation in this reading.
μὴ ἑαυτοὺς ἐκδικοῦντες, ἀγαπητοί, ἀλλὰ δότε τόπον τῇ ὀργῇ, γέγραπται γάρ· ἐμοὶ ἐκδίκησις, ἐγὼ ἀνταποδώσω, λέγει κύριος.
The OT quotation comes from
Vengeance is mine, and recompense,
for the time when their foot shall slip; for the day of their calamity is at hand, and their doom comes swiftly. (Deuteronomy 32:35).
However, the Septuagint renders this verse in a different way.
ἐν ἡμέρᾳ ἐκδικήσεως ἀνταποδώσω, ἐν καιρῷ, ὅταν σφαλῇ ὁ ποὺς αὐτῶν, ὅτι ἐγγὺς ἡμέρα ἀπωλείας αὐτῶν, καὶ πάρεστιν ἕτοιμα ὑμῖν. (Deuteronomy 32:35 LXX).
Roughly, it can be translated as
In the days of punishment, I shall recompense, in a time wherever their foot should trip, for the day of their destruction is near, and at hand prepared for you. (Brenden)
Therefore, it seems to me that Paul was translating directly from the Hebrew text, instead of copying from the Septuagint. He should be competent enough to do so.
The next verse continues
No, "if your enemy is hungry, feed him; if he is thirsty, give him drink; for by so doing you will heap burning coals upon his head." (Romans 12:20)
ἀλλὰ ἐὰν πεινᾷ ὁ ἐχθρός σου, ψώμιζε αὐτόν· ἐὰν διψᾷ, πότιζε αὐτόν· τοῦτο γὰρ ποιῶν ἄνθρακας πυρὸς σωρεύσεις ἐπὶ τὴν κεφαλὴν αὐτοῦ.
This quotation comes from
If your enemy is hungry, give him bread to eat; and if he is thirsty, give him water to drink;
for you will heap coals of fire on his head, and the LORD will reward you (Proverbs 25:21-22). The Septuagint translates it this way.
ἐὰν πεινᾷ ὁ ἐχθρός σου, τρέφε αὐτόν, ἐὰν διψᾷ, πότιζε αὐτόν,
τοῦτο γὰρ ποιῶν ἄνθρακας πυρὸς σωρεύσεις ἐπὶ τὴν κεφαλὴν αὐτοῦ, ὁ δὲ κύριος ἀνταποδώσει σοι ἀγαθά (Proverbs 25:21-22 LXX).
They are nearly identical. The Septuagint author and Paul used different words for 'feed' and both of them left out the word 'bread' and 'water' which are found in the Hebrew text. Did Paul copy from the Septuagint Proverbs or did he translate it all by himself just like what he did one verse earlier, rendering nearly identical translation?
It is beyond my ability to decide. Let the experts handle it. As for me, it is already hard enough to follow Paul's advice literally. Of course, to suffer patiently is heroic indeed. The only support one can muster is to believe that vengeance is God's. God will take care of injustice.
My Advocate, like the June 4^th and Sichuan victims, we may not be able to see justice vindicated for ourselves. So, let us rest in the satisfaction that You will take care of it.
Our Lady, when you saw your Son suffer on the cross, you firmly believed that it was God's plan to save the sinful world in this manner. May we see what you see and keep reflecting them in our hearts like you. Amen.