ah I see, sorry misunderstood. Well I tried to run that rivastats app but system blocked it for some reason, even if I ran it as an administrator, so I'll need to investigate that.
I've not had a crash since I posted it did 13 hours ago, and like I said I was playing Witcher then for about 20 minutes when it happened, but then I played it late last night for 2 hours without it crashing, so I reckon its quite random.
So it doesn't seem like it's the GPU, and I also ran a bench on CPU-Z and the temp on there was 54 C. Which I presume is within acceptable limits.
So, if it happens again, then could be talking PSU or mobo, from what I've read anyway.