hmmm .... i use qoverclock. i think the maximum you can increase it the mhz to is 236 or so ... 30mhz more than stock. i've never run into any issues with heat.... the main issues with overclocking are going to be battery life. if the processor is using up more energy, your battery will lose it faster. however, with the overclocking tools i've seen, there's also the ability to underclock the cpu allowing for the opposite effect.
~jason