When you decrease GPU power limit, GPU core clock speed decreases in games, and when you increase it, it gives maximum core clock speed value (or close) in games. For AMD GPUs, GPU power limit is usually as high (and low) as -50% and +50%. This way, you decide whether to choose the highest performance or the lowest temperature and noise. You can achieve higher GPU clock speeds with lower TDP when you undervolt the GPU. So with undervolt, performance increases, so GPU temperature decreases.
So it will be more accurate to determine the power limit according to the temperature and noise value. According to stabilization, giving the lowest possible voltage will provide performance.
Also giving maximum power to the GPU will also overload the PSU. Not only this! VRMs of the graphics card may be damaged over time and this is dangerous.
And there's that... Game performance depends on video memory bandwidth and number of shader units of a GPU. This means that there will not be loss of performance in the ratio of the power limit value.
