Here an old table frequence :
//////////////////////////////////////////////////// 
// CPU FREQUENCE FOR GP32 // 
//////////////////////////////////////////////////// 
// By ThunderZ // 
//////////////////////////////////////////////////// 
// Thanks to all GP32 community for make this // 
// table possible. // 
//////////////////////////////////////////////////// 
// WARNING, you use it at your how risk !!! // 
//////////////////////////////////////////////////// 
/* 
1 - 16.7 Mhz 
2 - 33 MhZ (1) 
3 - 33 Mhz (2) 
4 - 67.5 Mhz 
5 - 80 Mhz 
6 - 102 Mhz 
7 - 132 Mhz 
*/ 
int clock_settings [7]={16500000,33000000,33000000,67500000,80000000,102000000,132000000}; 
int div_settings[7]={ 0x71142,0x24003,0x3a013,0x25021,0x48012,0x1a020,0x3a011}; 
int clockdiv_settings[7]={0,0,0,2,1,2,3}; 
And here the function i use in my emu :
// pour overclock 
#define CLOCK40 0 
#define CLOCK66 1 
#define CLOCK133 2 
#define CLOCK156 3 
#define CLOCK166 4 
void SetClockSpeed(int nClockSpeed); 
void SetClockSpeed(int nClockSpeed) 
{ 
// clkdvn MCLK HCLK PCLK 
// 0 1 1 1 
// 1 1 1 1/2 
// 2 1 1/2 1/2 
// 3 1 1/2 1/4 
switch (nClockSpeed) 
{ 
case CLOCK40: 
// 40, 3 
GpClockSpeedChange (40000000, 0x48013, 1); 
break; 
case CLOCK66: 
// 67.8, 3 
GpClockSpeedChange(67800000, 0x69032, 3); 
break; 
case CLOCK133: 
// 133, 3 
GpClockSpeedChange(132000000, 0x3a011, 3); 
break; 
case CLOCK156: 
GpClockSpeedChange (156000000, 0x2c001, 3); 
break; 
case CLOCK166: 
GpClockSpeedChange (165000000, 0x2f001, 3); 
break; 
} 
}