I can send source code on request. Use this program at your own risk and backup before running it.
Program allows to manually adjust L, M, N parameters for Imate running 1.72 ROM (I have not tested older ROMs). The L parameter modifies SDRAM frequency (36 is a maximal value for my device), M - is a CPU frequency multiplier (shoul be left as a 4), N is a turbo mode for a normal mode multiplier. Setting its value to 1.5 makes the device work slower (though reported speed by PocketHackMaster and other tools is 796Mhz). My best results are 36/4/1 (530 Mhz) as shown on screenshots:
You may try other values. The smaller values may give the higher speed.