see how high you can go until you find a setting that renders the board unstable.
Overclockers have always puzzled me. The manufacturer knows exactly which are the critical pathways in the CPU. They can test and appropriately speed-grade their chips by exercising these pathways. Intel turbo-mode is supported, meaning that Intel has tested your CPU at the highest turbo speed they support. You'll get correct results, as long as you stay within the thermal envelope.
But if your CPU has not been manufacturer-tested at the speed you are clocking it., all bets are off. Which matters most - getting the right results, or getting wrong results faster?
It's not an entirely rhetorical question. If you are rendering frames for a movie or game, wrong results are either immediately obvious or of no significance. However, that's a special case. One bit wrong in the allocation bitmap of a filesystem, or in the compression or encryption of a datastream, and the eventual loss may be huge. Even in a render farm, overclocking has risks: it's the same overclocked CPU crunching the pixels, and adjusting the allocation bitmap of the disk on which the results are stored.
So the question: why overclock a Pi, when you can so easily buy a faster system?