(1) The bandwidth is being entirely consumed. It is all needed and the process is performing nominally.
(2) The bandwidth is being entirely consumed, but it might only be because the process is misbehaving and consuming more bandwidth than necessary.
Speed only translates to performance if the resource being quickly consumed is actually needed. Example-- a game might always use all CPU cycles, but only when rendering the most challenging scene is reaching peak performance.
Is that difference how people would actually understand the word? I've never (knowingly) heard it used like that. Certainly terms like "CPU utilization" and "network utilization" are frequently used to denote a simple use-divided-by-capacity ratio.
For your game example, I don't see what isn't encompassed by "speed" (how many FPS you get out) or "efficiency" (how much CPU/GPU you use to do it).
What's the difference between speed and performance here?