Thanks, seems like I'm on the right one now then!
Ok so blend fails on 2 cores after only 8 minutes, my initial thought was that the vcore (1.2375v) is too low but I managed 10 passes on IBT at max settings so this makes me think otherwise. I am using 4 sticks of RAM for the first time so maybe the NB needs more juice, it's at 1.3v atm.