yeah the higher you set the clock, the hotter itl get. for powersave just set the max lower (im not sure what TW powersave underclocks it to) just set max as low as the phone will function for txts and calls for power saving.
think No Frills has a safety thing so that if the phone crashes, it will go back to default settings to prevent a boot loop so youre pretty safe to mess around.
theres also stability test apps (cant remember any names) to really push the phone and see if it remains stable at whatever clock speed u have it at
just looked at your screenshot... DONT check that box until you know the settings are stable mate
global s3, UK. Ask me anything and ill reply even if its just an intelligent (or stupid) guess