Last month I got a Dell OptiPlex 5250 AIO (i5-6500 | 8 GB RAM | HD Graphics 530) from my work as they were just going to throw it out, I brought it home, immediately wiped it and installed Linux Zorin on it, and did some stress testing. After about 15 minutes it was overheating (sometimes hitting 97 C) on it's stock hardware. Repasted and tried again, same results only it lasted a little longer, about 30 mins this time. I decided I was going to make this work. I ended up buying an i9-9900k, removed the stock heat sink and fan, and I wired an old Cooler Master closed loop to fit the laptop connector on the motherboard. I was a little worried about trying to run both the fan and pump on the same fan header due to power consumption, so I ended up wiring an old fan so that rather than it being a PWM connector it was a USB, and plugged it into a USB 3.0 port. The CPU now sits at around 74 C and is extremely stable even at full load over extended periods of time. It is absolutely an eye sore, it looks dumb, but it is possibly the best pc build I've done.