Overclocking GPU on raspberry pi 2 model B?

Question

I'm trying to overclock the GPU on my raspberry pi 2, but I can't seem to find out how. Also, there's no setting for it in config.txt? Does anyone know where I might be able to find this setting (other than in the raspberry pi configuration tool, unless someone could tell me how high to set the GPU to overclock it) so I can modify it? Oh, and if it makes any difference I used the Raspberry Pi Configuration tool to overclock to 1000 MHz. Thanks :)

CURRENT SETTINGS:

In config.txt:
core_freq=500
sdram_freq=500
over_voltage=2

In the Raspberry Pi Configuration tool:
Overclock: 1000MHz (High)
GPU Memory: 64

Answer 1

On my Raspberry Pi3 with heatsink (and fan when necessary) I increase the gpu frequency to 500.

gpu_freq=500

gpu_freq sets core_freq, h264_freq, isp_freq, and v3d_freq

https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md