Why wouldn't it run a subset of tests on each boot? It seems like it would be silly not to. That's probably one of the mechanisms by which the bios will automat

Why wouldn't it run a subset of tests on each boot? It seems like it would be silly not to. That's probably one of the mechanisms by which the bios will automatically revert to "safe" settings after a botched overclock. You could do an experiment. Remove some of the RAM modules and see if the 20 second boot time decreases.