An aside - if we're only going to stick with what we see on-screen, Trek Tech would be pretty slow
On-screen, it's respectable depending on where you're at.
TOS speed data appears to be dependent on location.
- TOS interstellar speed go up to the 770,000c range.
- TOS near star speed drop well below 10c range.
- TOS intergalactic speed is in the 900c range.
TNG's speed data doesn't appear to be dependent on location.
- TNG Warp 9 speeds is in the 830c range.
- Voyager Warp 9.9 speed is up to 21,000c.