Ah, gotcha. I've only ever worked with mobile AMD cards so I didn't know it was changed.
When you edit the config file for high performance, editing the global file will set it to max performance all the time, but creating and editing a config file for Dolphin will make it run at the higher clocks just for Dolphin and idle all the rest.
Dolphin doesn't always send the command for high performance needs to the GPU, so it keeps the GPU at low speeds when a game may need them to be higher.
When you edit the config file for high performance, editing the global file will set it to max performance all the time, but creating and editing a config file for Dolphin will make it run at the higher clocks just for Dolphin and idle all the rest.
Dolphin doesn't always send the command for high performance needs to the GPU, so it keeps the GPU at low speeds when a game may need them to be higher.