[feathers]

Yes.. Never go more than 20 amps above a peltier's maximum rating or more then 4000 volts on a 20 volt unit.

So why don't we apply this 'do not exceed' rule to overclock voltages and speeds?

Absolute ratings are indeed there for a reason but often you will find there is a little bit of tolerance beyond the rated limit.

And it do depend on the situation a component finds itself in..

Max ratings for voltage/current are quoted at a certain temp range.

If your component is operating at a much lower temp then you can usually buy yourself some extra capacity.

In essence: A peltier rated at 15.2 amps isn't likely to be adversely affected by an increase to 15.3 or 4 (or perhaps higher). Same applies to voltage. Especially if said peltier is watercooled.

Same applies to any electronic component. I've had a P4 2.4 core voltage raised to 1.9 volts. This is far in excess of it's rated voltage. I was able to do this because the CPU was being chilled close to zero celsius. I would not have pushed the voltage so far had I been cooling with heatsink/fan or just plain water.