Problem was definitely not CPU temp - that was one of my first thoughts and I ruled it out pretty quickly.
The problem, apparently, was an outdated BIOS... at least following updating that I have had over 10 hours of glorious uninterrupted play. So now I feel like a complete moron - spent literally hours and hours trying to fix and a 15 minute BIOS update that I had put off as a 'get to it eventually...' type job sorted it!
Thank you both for taking the time to answer though - appreciate it a lot
