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).