If 1 of 8 workers fails, especially during small fft then it's cpu voltage. Bump it once or twice. As for the other tests, I don't know what their errors mean. Linpack/IBT/LINX all produce errors which are hard to determine. That's why I dont like them. If it fails during large fft then its probably memory error you can try running memtest/upping ioh. I would try running small fft at that point for a good amount of time and make sure its not the cpu voltage. If it passes 8-12 hours of small fft then work on making it pass large fft. Just remember to keep track of your settings.