There's no such thing as a GPU utilization % per se. Perf counters are much lower level (e.g., number of quads passing through some interface or cache hit rates in some cache). Fences are actually a better metric since they give you an idea of how much work is scheduled to execute rather than a snapshot of what various blocks are doing.
Right. Adjusting power management based on the work that is going to be done always seemed a lot smarter than adjusting it based on what you just finished doing