No two cpu chips are made the same. Saying that, some will require less voltage to reach those higher cpu speeds. Those who are fortunate enough to be able to run a low voltage kernel at their desired clock speed will experience lower cpu temperatures than someone who has to run a higher voltage kernel.
To figure out which is best for you, start with a low voltage kernel one slot above what you want to run. If your phone runs stable at that speed, you should be fine running a low voltage kernel at the clock speed you wanted. If your phone does notboot or all applications start to force close when you do boot, try lowering the clock speed or going up to a medium voltage kernel by flashing a new kernal. No one should have to run a high voltage kernel unless their cpu chip totally sucks. :icon_ devil: