125Mhz comes from https://bugs.maemo.org/show_bug.cgi?id=7116 (as you can see, testing firmwares had scaling_min_freq set to 125Mhz). There has also been comments about that on IRC
720Mhz comes from the 3530 datasheet, which is public. It also indicates it should be run at the same core voltage as 600Mhz, which may or might not apply to the 3430... Actually, seems that only applies to newer 3530s.