I'm starting to read the Light Novel from Kumo desu ga now and Volume 4 instantly gave us a better speed feat.
Something just appeared here.
It didn't even teleport. It was just that fast.
The explosive sound was the impact of its arrival.
There was nothing in my range of vision just seconds ago, and now something arrived from outside that range so quickly that it caused a powerful shock wave.
|~ Kumo desu ga Light Novel, Volume 4 Chapter 7|
The person who appeared here was the current Demon Lord Ariel, stat wise the second most powerful being within the System (and the most powerful in total).
What's interesting is that she appeared from outside of Kumoko's vision range in a timeframe that seemed like teleportation. In fact later in that chapter Kumoko goes as far as to say "that she could imitate teleportation just by running".
That means the timeframe of her arrival was considerably short. Seeing that Kumoko, who at that point can easily dodge arrows, didn't see her comming she should have been within Kumoko's Detection range for less than 1 second.
Detection is a skill that lets Kumoko perceive all kinds of things all around her. In particular it has a Danger Perception that warns her if a powerful opponent, like Ariel here, approaches her.
Volume 4 also gives us a sense of what the range of Detection is:
My thoughts are interrupted by Danger Perception going off alarmingly.
My whole body stiffens, warning me that I'm in danger.
At the edge of my vision, I see a torrent of black energy.
It resembles Araba's full power breat attack but with a different attribute and far more powerful.
I'm guessing that was the Dark attribute.
And it was even stronger than Araba's full-powered breath attack.
Not to mention, this was launched from miles away.
|~ Kumo desu ga Light Novel, Volume 4 Chapter 3|
As seen in this quote Kumoko's Danger Sense warns her of Mother when she is still miles away. Miles means 2 at least.
2 miles = 3218.69m
So this is the distance Ariel would have to cover in a timeframe too fast for Kumoko to react to.
Going with 1 second this means
3218.69m / 1 s = 3218.69 m/s = Mach 9.38393586
Upper ends of Hypersonic.
Scales from Ariel, to Wrath and Gods.
But wait, there's more. Later on in the chase with Mother which we used to judge the Detection range we get following
The distance between us is around half of where it started a minute ago.
In other words, she'll catch up to me in another half a minute.
The Teleport should be ready just seconds before that.
As long as I don't screw this up, I'm gonna make it!
But seriously, I better not screw this up.
Mother starts activating magic spells as she runs.
I'm working on a spell while I run, too, so I guess I can't complain this time.
I can't, but I want to!
Judging by the looks of it, Mother is using the Dark Magic spell Dark Bullet.
It's a simple spell, the weakest of Dark Magic.
That's all well and good, but the amount of shots and their range are definitely not normal.
The greater the range of the magic, the weaker it becomes.
If Mother wants to damage me from several miles away, she'd have to use a huge amount of MP.
The last sentence indicates that at this point Mother is still several miles, so at least 2, away from Kumoko.
And the first sentence states that this is half of the original distance.
So if half the distance is at least 2 miles, than the original several miles distance must have been at least 4 miles. This corrects the range of Detection to 4 miles.
4 miles = 6437.38 m
6437.38m / 1 s = 6437.38 m/s = Mach 18.76787172
Extra: Confirming the Subsonic rating
Kumoko is currently rated as Subsonic based on some hard to evaluate feats.
However, by the quote in the above section Mother covered half of at least 4 miles, so at least 2 miles, in half a minute.
2 miles / 30 s = 3218.69m / 30 s = 107.2896666666666667 m/s = Mach 0.31279786200194359402
Of course it's actually higher, since Mother decreased the distance between herself and Kumoko by that amount and Kumoko was running away.