Thanks for the feedback.

I think I'm definitely going to remove the heatsink and check the contact on it as it sounds like it's definitely running hot as I am only at 191BCLK and stock IOH volts at the moment.

Also, the fact that it stays at a high temp even after stopping the stress testing suggests to me that there is little or no contact with the heatsink. Maybe the pipe is stopping it from sitting correctly as jetroho found with his.