Elf scaling part 1:
Here's what I've found on the scaling for the Elves in the Third and Second Ages. Galadriel's section is especially long as Tolkien kept revising his opinion on her.
Gil-galad:
Explicitly scales to Sauron at the time of the Last Alliance
"Gilgalad and Elendil are slain in the act of slaying Sauron." - Letter 131
"Against Aeglos the spear of Gil-galad none could stand; " - AKALLABÊTH: Silmarillion (No cause for contradiction, none of Sauron's army could singlehandedly fight Gil-gald, likely including the Nazgûl, who were mentioned in APPENDIX B's section on the aftermath of the Last Alliance, but definitely including werewolves, who in the First Age could fight High-Elves lords).
"But at the last the siege was so strait that Sauron himself came forth; and he wrestled with Gil-galad and Elendil, and they both were slain, and the sword of Elendil broke under him as he fell. But Sauron also was thrown down..." - AKALLABÊTH: Silmarillion (A more detailed version of the first)
Galadriel:
She has a lot more potential for variety. Galadriel doesn't fight much in Tolkien's Legendarium, so we have little in the way of direct scaling beyond description. That being said she is repeatedly described as the "greatest" of the Noldor besides Fëanor, but at other times she's described as the "greatest" of the Elves left in Middle-Earth.
She definitely scales above Elrond as a result and likely should scale above Glorfindel. However, Gandalf the White claim to be second only to Sauron in the Two Towers, with a later claim from himself stating he might be rivalled by the Witch-King in Return of the King. Moreover, Tolkien's Letters assert Gandalf the White's superiority over her. The issue with this series of statements is that Glorfindel's presence alone causes the Witch-King to flee.
My personal solution to this is Gandalf (W) >/= Witch-King = Glorfindel with Galadriel being weaker than Gandalf, but only just a bit above Glorfindel. It's very finicky and imperfect, but Tolkien's structure never works well with this sort of thing. Moreover, Glorfindel was only posited as being this strong in the last bits of Tolkien's writing, so you could just have him scale above Galadriel and have it as that.
"Galadriel, the greatest of the Eldar surviving in Middle-earth..." - II: THE ISTARI: Unfinished Tales
""In Lindon south of the Lune dwelt for a time Celeborn, kinsman of Thingol; his wife was Galadriel, greatest of Elven women.""
"Galadriel was the greatest of the Noldor, except Fëanor maybe, though she was wiser than he, and her wisdom increased with the long years. "
IV: THE HISTORY OF GALADRIEL AND CELEBORN: Unfinished Tales + APPENDIX B: LOTR
"‘Dangerous!’ cried Gandalf. ‘And so am I, very dangerous: more dangerous than anything you will ever meet, unless you are brought alive before the seat of the Dark Lord." - THE WHITE RIDER: LOTR
"‘Then, Mithrandir, you had a foe to match you,’ said Denethor... ‘It might be so,’ Gandalf answered..." - THE SIEGE OF GONDOR: LOTR
"Of the others only Gandalf might be expected to master him – being an emissary of the Powers and a creature of the same order, an immortal spirit taking a visible physical form. In the 'Mirror of Galadriel', 1381, it appears that Galadriel conceived of herself as capable of wielding the Ring and supplanting the Dark Lord. If so, so also were the other guardians of the Three, especially Elrond. But this is another matter. It was part of the essential deceit of the Ring to fill minds with imaginations of supreme power."
+
"In any case Elrond or Galadriel would have proceeded in the policy now adopted by Sauron: they would have built up an empire with great and absolutely subservient generals and armies and engines of war, until they could challenge Sauron and destroy him by force. Confrontation of Sauron alone, unaided, self to self was not contemplated. One can imagine the scene in which Gandalf, say, was placed in such a position. It would be a delicate balance."
- Letter 246 (Only Gandalf was capable of truly matching Sauron, even in a scenario where all three had claimed their own individual One Ring. Elrond and Galadriel could not individually match Sauron in this regard, only Gandalf).
Glorfindel:
Dues and performs a mutual kill with a Balrog in his First key. In his second key, he is confirmed to be stronger than before, and is described as a peer of the Maiar. This doesn't do much tier wise, unless a description of the Maiar he is compared to exists. Notably he is outright unable to withstand the collective might of all 9 Nazgûl, although a seperate quote attributes this as mainly being due to the Witch-King. He does intimitate the Witch-King during the Fall of Angmar, but it's not certain if he's as powerful as he is in the Return of the King.
First Key
"Many are the songs that have been sung of the duel of Glorfindel with the Balrog upon a pinnacle of rock in that high place; and both fell to ruin in the abyss."
OF TUOR AND THE FALL OF GONDOLIN: Silmarillion
"Then sprang the Balrog in the torment of his pain and fear full at Glorfindel, who stabbed like a dart of a snake; but he found only a shoulder, and was grappled, and they swayed to a fall upon the crag-top. Then Glorfindel's left hand sought a dirk, and this he thrust up that it pierced the Balrog's belly nigh his own face (for that demon was double his stature); and it shrieked, and fell backwards from the rock, and falling clutched Glorfindel's yellow locks beneath his cap, and those twain fell into the abyss." - HISTORY OF MIDDLE-EARTH (One of the several versions of events written regarding the battle)
Second Key
"On foot even Glorfindel and Aragorn together could not withstand all the Nine at once." - Many Meetings: LOTR
"For even the Wise might fear to withstand the Nine, when they are gathered together under their fell chieftain" - THE COUNCIL OF ELROND: LOTR
"‘But it is said that when all was lost suddenly the Witch-king himself appeared, black-robed and black-masked upon a black horse. Fear fell upon all who beheld him; but he singled out the Captain of Gondor for the fullness of his hatred, and with a terrible cry he rode straight upon him. Ea¨rnur would have withstood him; but his horse could not endure that onset, and it swerved and bore him far away before he could master it."
+
‘Then the Witch-king laughed, and none that heard it ever forgot the horror of that cry. But Glorfindel rode up then on his white horse, and in the midst of his laughter the Witch-king turned to flight and passed into the shadows.
APPENDIX A (The top bit is there for context, as whilst the Angmar's army had been destroyed, the Witch-King himself had no reason to run and was seemingly a threat to the whole army. It was only when Glorfindel appeared that he ran).
"We could then reasonably suppose that Glorfindel (possibly as one of a small party,(1) more probably as a sole companion) landed with Gandalf - Olorin about Third Age 1000. This supposition would indeed explain the air of special power and sanctity that surrounds Glorfindel - note how the Witch-king flies from him"
We can thus understand why he seems so powerful a figure and almost 'angelic'. For he had returned to the primitive innocence of the First-born, and had then lived among those Elves who had never rebelled, and in the companionship of the Maiar (2) for ages: from the last years of the First Age, through the Second Age, to the end of the first millennium of the Third Age:"
"For long years he remained in Valinor, in reunion with the Eldar who had not rebelled, and in the com- panionship of the Maiar. To these he had now become almost an equal, for though he was an incarnate (to whom a bodily form not made or chosen by himself was necessary) his spiritual power had been greatly enhanced by his self-sacrifice."
LAST WRITINGS: HISTORY OF MIDDLE-EARTH (Some of Tolkien's last writings
Summary
Gil-Galad = High 7-A, likely Higher
Galadriel = either 7-A, likely Higher, or Likely 7-A, likely Higher (if downscaling from Witch-king and Glorfindel), or something else. Maybe she's comparable to Gandalf? She does have her own feat in destroying Dol Guldur
Glorfindel = Low 7-B, likely Higher (First key) and 7-A, likely Higher (scaling to the Witch-King)
