I've been unable to find joy by over-clocking my PR1.2 device via the kernel-power-settings package:

Background:
I enjoyed noticeable performance and battery gains via Titan's OC-kernels before flashing to PR1.2. I also tried the leaked PR1.2, encountered reliability issues with Exchange Server syncing, and this reverted to the non-overclocked vanilla PR1.1.1 with the up-flashed radios.

It was this install that I then flashed with the official US-version PR1.2, including the vanilla eMMC using flasher3.5exe.

Results:
Attempts to overclock this install via Titan's kernel-power-settings produced frequent system freezes in the browser, in the phone app, in the email app, and when resuming from sleep via the side-slider button (i.e. system would not resume). In all cases of system freeze, I resorted to pulling/re-seating the battery in order to reboot each time.

The only power-settings I explored while doing this were based on the Ideal settings, with limits set to 125/750, 125/850, 125/950, 250/750, 250/850, and 250/950.

Outcome:
I've since de-installed kernel-power-settings and am now running a fresh PR1.2 flash. Battery performance is excellent: as of 5pm today with 8 hours of constant Wifi/3G connectivity and moderate email, browser, witter usage the battery is still close to max.

YMMV.