Update: In my case it seems to have been overheating/overclocking that caused the access violation errors. I did a thorough clean on PC today, applied new thermal paste and downtuned to 4ghz and managed to play 3 CW campaigns in a row without crashing using 3 threads.
That being said, from past experience and having run 8 threads before just fine, I think something has been left unoptimised or god knows what, as temperatures at even lowest settings are pretty high. I’m saying this after the first time around i got crashes every 2 minutes, seems to have been uneven thermal paste/MSI afterburner. I was more worried about temps before but i’ll keep an eye on CPU usage tomorrow, but the cores were definitely not being utilised at high %'s.