Is there a difference between "pace" and "speed"? I have a feeling that with "speed" we usually specify the actual value, while with "pace" we talk more relatively. Am I right?
Yes, you are right.
Instead of speed you could use the word velocity. Either should include velocity units (distance units / time units) whenever mentioned.
Pace gives a relation to others performing the same task.
- Set the pace.
- He's not keeping pace.
- I can't work at the same pace.
- We have a pace setter for our 5k run.
- The pace car is on the track.
In the context of running, "pace" can mean the inverse of speed. I.e., whereas speed is measured in units of distance per unit of time (e.g. miles per hour), pace is measured in units of time per unit of distance (e.g. minutes per mile).