With GPU rendering, you should learn about GPU processing and memory usage too, not that it would matter much for such a use-case.
nvtop is nice for displaying all that info (it's not nvidia-specific).
Also % CPU usage is not a good metric, especially when most people forget to set CPU frequencies to fixed values before measuring. And heterogenous architectures (e.g. big.LITTLE) make such numbers meaningless anyway (without additional context). But again, none of this really matters in this use-case.