It's not rocket science. I've run a 30% overclock on a machine with 80% daily uptime on air and saw it BSOD like twice over 4 years. Also as some other people in this thread have mentioned, modern CPUs will overclock themselves, and if you undervolt you can get quite a lot of headroom, especially if you get lucky with binning. With that headroom and some hackery (Throttlestop is often all you need) you can get modern chips to hold all core turbos indefinitely. YMMV but I've managed to hold a stable 35% increase in sustained processing power without running too close to the thermal limits.