From LedHed's Wiki
Overclock
# Custom Overclock arm_freq=1333 over_voltage=5 gpu_freq=550 sdram_freq=525 sdram_schmoo=0x02000020 over_voltage_sdram_p=6 over_voltage_sdram_i=4 over_voltage_sdram_c=4 #dtoverlay=vc4-kms-v3d # Turn off over temp and under volt square avoid_warnings=1