CPU-Multiplier Overclocking causing (silent) data corruption?
Running any device beyond its rated specification means you have no guarantees of said device performing as intended.

Whether or not it fails (death, data corruption, dodgy calculations, brewing coffee instead of tea, etc.) depends as much on the direction of the wind as anything else. You are the proverbial guinea pig.

If the manufacturer hasn't guaranteed the specifications beyond a certain point, it is usually because either they haven't tested it under said conditions, or because the mean time before failure (MTBF) is too low for those conditions. MTBF is essentially the average time before a failure is expected - it doesn't mean all devices will survive to that point or die after that point, just that they will on average.



In terms of what effects you might see when overclocking, well, pretty much anything. 

When chips run hotter, or are clocked faster, propagation delays through the chip start to take up a higher portion of the clock period. If these delays become too long you end up with data setup violations - basically where data signals arrive at registers after the clock that was supposed to clock them.

Setup violations cause all sorts of random effects. Calculations start returning incorrect values as bits in the data paths get misread. Instructions execution might be incorrect if there are violations in the instruction pipeline. Your comparison instruction that determines whether or not to launch the worlds nuclear arsenal might be miscalculated. Your precious homework report might get corrupted as data is passed to storage controllers incorrectly.

There is really no telling what will happen. And more problematically it might happen on one chip at a certain frequency, but not on another due to process variation.