We overclock/overstress parts when there's a substantial payoff. One Freescale uP is rated for 16 MHz clock, actually gets wonky at 44, so we run it at 20. One microwave schottky diode is rated for 2 volts reverse, leaks a bit at 7, so we use it at 4. Adding a heatsink to an FPGA can buy some timing margin. Some diodes and cmos parts leak four or five orders of magnitide less than the datasheet guarantees. An
0603 resistor can dissipate a quarter of a watt safely. The trick is to take calibrated risks where there's demonstrated margin and big paybacks, and take zero risk everywhere else.John