Speed-wise this appear to me to be about the same speed 8MHz 68000 Mac SE did run it's graphics.
https://www.youtube.com/watch?v=0wDtxYeJdzg (8-Bit Guy)
It worked with N drives, too, although the C64 sort of had to act as the bus master to avoid serial packet conflicts.
That was a long time ago and I’ve certainly forgotten many of the details. But it won me a trip to the International Science Fair (this was before Intel started sponsoring it).
The variables never moved in 30 years. Stop adding visual effects if all you aim for is operational swiftness.
This OS on the other hand is a desktop OS for an ancient 8-bit processor (far less capable than modern microcontrollers) and oriented around the user interface.
So... not much to compare really, they're completely different beasts.
Shame too, because ANSI artists could have done some even more impressive works with the PETSCII character set but the world had already moved on by that point.
In theory quite portable to other 'new' 6502/816 systems.
I never got the chance to use it on a real C64, but I played with it a lot under CCS64 ( http://ccs64.com/ ). I had a very slow computer at the time, too slow to run many modern games and applications, so I found a lot of interesting things to do under various emulated environments.
Edit: since we're mentioning (possibly) obscure operating systems, WingsOS ( http://wingsos.org/ ) also deserves a note :-).