CPUs sold under the same name can have substantial differences in their overclocking headroom. Back when variation was larger, purchasing a new CPU was thus participating in the "silicon lottery", at least if you wanted to OC.

The siliconlottery site used to buy a whole lot of CPUs, test them, determine their max stable overclocks, and then sell the good ones at markup (and the not-so-great ones at a little below market). If you wanted the very fastest cpu money could buy, and didn't want to start binning cpus yourself, they were the best option.

The market has largely died out because the manufacturers have improved their binning and reduced variability to the point that the best chips are no longer meaningfully better than the average and OC rarely makes much sense anyway. In many ways, this is good for customers, but it is an end of an era.

Looks as if they bought CPUs and did their own benchmarks/binning and resold them based of their measured performance.

Looks like you could mail them a CPU and pay them to upgrade the thermal compound under the IHS and optionally test it to determine maximum stable overclock parameters.

It looks like they also binned high-end CPUs. For those not familiar, that means they tested each CPU to determine its maximum stable overclock, then re-sold them with a markup on the fastest ones.