Use Throttlestop to undervolt the CPU. YMMV, but a good starting point may be -100mV for CPU, Cache, and iGPU. For overclocking the GPU, I actually set mine to a desktop default speeds and cap my framerate at 60FPS. Temps remain in the high 70s under full load for both the CPU and GPU. I see no reason to raise GPU clock speeds higher than desktop defaults.