[5* Artifacts have a 100% dropchance on AR45 domains. Sometimes (very little chance from what I can tell because it only happened twice for me so far), even 2 can drop on AR45.
If you have shitty ones, artifact farming on AR45 is the way to go because if you have bad ones, gaining +10% dmg from artifacts is way cheaper and easier to do than the 5-7% dmg you gain from leveling up your characters.
You can achieve that dmg gain from changing a single artifact and it doesn't even have to be god rolled.
Not sure if you want to "test" it on my guess but Noblesse should (and I'm basically 99,9% sure of that) buff every sword attack from his ult.
C6 works like this:
C0 - 2 swords 3 swords 2 swords 3 swords 2 swords 3 swords
C6 - 2 swords 3 swords 5 swords 2 swords 3 swords 5 swords
You can get 18 sets of swords easily.
Xingqiu has the highest amount of Q damage in the game at this moment.
You are looking at roughly 6000% dmg over it's duration at Rank 10 (C6) - obviously, with noblesse, it's 7200% (again, I see no reason why it shouldn't work).
While also adding like 40+% dmg reduction on each hit you recieve, while also adding interrupt-resistance.
And his E is the also hitting like crazy with and without constellations
So if you don't mind a guy in boy-scout pants and you are looking to min max. You should build him.
Anyone who says he is "bad" (and I've seen quite a few saying that, even in this thread) has *no* idea. He is probably the best overall unit in the game by quite a large margin.
He works amazingly well with Fire characters, because his E hits like a truck,
he works amazingly with Electro characters, because he will constantly reapply wet,
he works amazingly with Geo characters, if Ice is involved - shatter works with Geo,
and he works amazingly with ice characters (perma freeze),
he works amazingly with Anemo characters (like any element aside from Geo)
Water is the most versatile shit you can think of, and with enough ressources and energy recharge, you will apply it non stop. I'd recommend the Sacrificial Sword as a 4* weapon, Skyward as a 5* weapon.
But that's from a C0 perspective, at C6, his energy recharge might be high enough from the swords constantly regenerating energy. With 150% energy recharge (+50%) You are looking at 81 energy if every interval hits. Which means you have Cooldown limited uptime without gaining any energy orbs.
Since you are gaining energy orbs, you can go with 0% Energy Recharge imho.
edit: Scratch that last part, the 3 energy gain only comes from every 3rd set (5 swords) of his ult.
So yeah, Sacrificial sword it is (or any weapon with energy recharge)