well the phone will shut down before any damage can happen to it due to heat....i think i heard somewhere it was 135 degrees, but i could be wrong.
Slayher kernels are considered the best simply because they are interactive instead of on demand. interactive governers keep the processor going faster for a longer period, so it may be at 1ghz for a the entire duration of 4 button pushes. where "on demand" will only go up to 1ghz to process the one command, then going back down to the minimum.
because of the above, Slayher kernels seem faster in ever day use, but since the processor is chugging along longer, it not only gets hotter faster, it also eats battery faster.
for instance Chevys ULV kernel, i get great battery life, and it rarely gets over 105 degrees, but i hit 110 all day long on a slayher kernel.