"Correct Frequencies" can all depend on usage and the device, it's been covered lots of times before.

While I wouldn't recommend it to all, after long periods of testing different frequencies with my device and usage. I run 125-600 and have no issues with low battery or lack in usability. I have never experienced any issue with 125Mhz being unstable.

Bear in mind that since the "125Mhz unstable issue" was reported, smartreflex has been fixed and also there have been new releases of KP.

For reference this is the bugzilla link:-
https://bugs.maemo.org/show_bug.cgi?id=7116