Managed to get my computer up and running finally. Seems the problem was my Corsair H801 after all; turns out that despite it being a sealed system, it seems to have air in the pipes. It was causing my processor to run 20°C hotter than it would with the stock cooler. Thankfully, I still have that around, so my computer is running safely at a cool ~45°C.
This was originally a link to the Corsair website, however this is now a 404 error. ↩