Depends on the devices at the beginning and end.
The values possible from the standard are available here:
https://glenwing.github.io/adapters
I think the delay can be neglected at 3m.

As far as I know, the length (up to a certain length) has little to no effect on latency and flow rate. The best thing to do is to look at the DP1.4 HBR3 standard and what it can do.

I have not noticed any additional latency or the like at 1440p and 144hz.