Definitely go for speed. Glaive already has massive damage, whereas reducing the speed could be dangerous.

I don't find it's usually worth it to augment at all. The trade-offs you get for doing so almost exactly balance the return, so it's not generally helpful, in my opinion. There are some niche cases where you might want to do this: If you have a good enchantment on the weapon and want it to trigger more often, you might augment with speed; especially so if you have a +2-3 ring of accuracy. If it's a particularly quick weapon by default and has a lot of upgrades, it might start making sense to augment (though I haven't tested it, I doubt it). You might augment for damage if you're confident you can consistently perform one-hit kills and are not confident you can survive in a straight-up fight, but this sets you up for extremely messy failure if you do find yourself in such a fight.

As for whether to SOU, I'd take 2 more into it, then hit it with the upgraded Scroll of Remove Curse (whose name I forget) that you can get from the cauldron. When your item already has +6, those upgraded remove curse scrolls are more powerful than SOU, providing +2 levels per use. Make sure you save at least one remove curse scroll to get rid of the resultant curse on your item.

Before you do anything to that glaive, though, you need better armor. +1 chainmail may start to fall off soon.

Something that took me a while to figure out: If you find a shrine of healing, it will remove the curses from all of your equipped items as well as fully heal you. You can use this to your advantage by just equipping all of your unidentified items next to those shrines. If it gets cursed to you, no worries, just step in the shrine. If not, your item sells for a bit more now. Be advised, equipping takes a several turns, so if you're low on hunger just skip it or check the most important items.

Small nitpick: It's Aug Ment, not Ar Gu Ment.

Late but maybe will help in future runs: speed 100%. Usually augmenting weapons is unnecessary but in this case it's important. Spear and glaive have the advantage of being able to hit enemies with no damage in return thanks to their range but the slowness will cause you to skip a turn after every second attack and because of it you can't abuse the range reliably. Conveniently speed augmentation completely negates the speed downside so it takes exactly 1 turn to attack, so as long as you have a way to gain distance and no random enemies come in to interrupt you can kite enemies and continue poking them until they die forever. Some ways include the flow armor glyph, ring of haste (you had one in this run, very good) and circling around 1x1 pillars so enemies lose you (those generate in prisons which makes spear a great early game weapon)

I have been corrected: Removing the curse from the item also removes any bonus you got from applying the curse, so my previous advice about upgrading the scroll at the cauldron was mistaken and should not be followed.

I think I would go for speed.

What I love about SPD is that decision is dependent on many other factors making each game unique.

My last run used a +15 damage-augmented kinetic glaive. The highest damage I did was 258. It was great fun. Oh, but I had a Ring of Furor +3.

Augment*?