That's the problem, this was completely random, the system was just idling, and it's the first time it's crashed in months of stability, so I can't replicate it! The strangest thing is that, following the crash, the computer wouldn't boot at all until I pulled back my overclock, even though, again, it's been stable in much more CPU-intensive applications with decent temps for months now!
Since last night I had one more freeze this morning, but I'm not sure if it's the same source because this one did log in event viewer: "The file system structure on the disk is corrupt and unusable. Please run the chkdsk utility on the volume C:" Running chkdsk found some errors, but those might have been caused by last night's crash (if the system was writing to disk when it happened), so I can't be sure if my disk is the cause of it or not...
I had some stability probems a few months before, I was sure it was my HDD packing it in, and it turned out to be the SATA modular power cable. Soon as I used another one all my problems disappeared. I have a sneaking suspicion that this might be the same thing, as I just ran chkdsk again and it found some errors yet again, and two in the same day mean either the drive's packing it in or I'm having power problems again...