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It depends on the size, for something fairly large like smart dust or the various small microswarms centimeters per second is probably about right.
For really small swarms like saboteurs, disassemblers, proteans, taggants, guardians, maybe cleaners the speed is a lot slower. Centimeters per minute probably if they're under their own power. Those are going to get set up by something, and then they aren't going to move a lot.
Mites and bacteria are pretty good natural things to model micro and nanoswarm speeds on.
I've always imagined that TITAN nanoswarms had a number of larger micro-scale bugs which manufactured and commanded the smaller bugs, while networking with each other. I'd use swarmanoid movement rules to govern their speed, so they'd be quite quick, but still vulnerable to certain tricks.
Exsurgent femtobot swarms are basically space magic, and should be at least as quickly, assuming they don't coalesce into some more solid shape with legs or wheels or something and go really fast.