I've never experienced a bad CPU before, but I think I may have one in my i5-2500k... I need some help determining if the CPU is indeed going bad, and/or what other tests I can run to identify the problem. A little back story... I have run this CPU on a 24/7 overclock with a 0.075+ main voltage offset for years (all other settings on Auto). I have a Corsair Hyper 212 for cooling. Typical idle temps were in high 20c/low 30c range, typical loads in mid 50c, and stress testing got me to high 60c/low 70c ranges.
I began experiencing issues about a month ago, and at that time I reset everything back to stock settings. So all tests I have run have been on stock 3.3GHz and stock voltage.
The problem I am experiencing is with memory faults... Programs like 7zip (CRC), QuickPar (Verify Failed, Checksum Error, Memory Fault), Firefox/Chrome (random crashes all the time when just browsing text websites) and many others are giving me memory errors. I have unzipped the same files which are giving me CRC errors on a different system without any problems. I have also run QuickPar repairs that give me various errors on this main system - but the files are checked and repaired fine on another system (yet continually fail on this main system).
I put each 8GB stick of RAM into another system, and ran Memtest (4.3.5) for over 5 hours (3+ passes) on each individual stick by itself. All resulted in 0 errors. Then I put the sticks back into my main system, and ran Memtest (with all 4 DIMMs populated) for over 10 hours (3+ passes) - again 0 errors. This leads me to believe my motherboard (at least memory DIMMs) and RAM are okay. I have a PSU test, and I also tested my PSU (without load), and it says it's fine (but nothing indicates the PSU would be going bad). I unseated/reseated my GPU, RAM, and all SATA connectors - still have the issue.
As an additional example, I ran Prime95 (on stock settings, and after doing all of the other memory tests), and within 3 minutes, 3 of my cores fail with, "rounding was 0.5 expected less than 0.4" - Edit: And the 4th core failed after 36 minutes ("rounding was 0.4981994629, expected lass then 0.4")
From what I've read, all I can figure is maybe the L2/L3 cache is going bad on my CPU.
Any input, advice, knowledge would be much appreciated.
Thanks