I am assuming your EX1 project uses XDCAM EX whereas your problem project is using Cineform. Is this correct? If so, I think its a Cineform problem. You can either reinstall Cineform or use HDLink to re-render the original video and maybe divide it into 2 30GB files. Since your XDCAM EX project works just fine, then I'd put money on Cineform being the cause of this start-stop problem.

The successful render of the EX footage was actually from HD footage that was in a PAL DV sequence and scaled down in Premiere to SD resolution and output as PAL DV. It's a long story as to why I did it that way, but that's what I did.

I'll sneak home in an hour or so and try the render of that project in an XD CAM EX project setting and export at full resolution as an MP4.

It possibly is Cineform causing the problem, but I don't know why it would... it's usually a solution for my problems rather than a cause.

I'll do some more tests.

UPDATE:

Export of full HD MP4 from EX timeline resulted in non-stop 76-75% uninterrupted process use. No starts and stops.

So it looks like it could be a Cineform thing.

Another update:

Re-seated the heatsinks and now things are working fine. They're in the same formation as before. You can't rotate them 90 degrees - they only go one way. I used the advice in the PDF that David provided - applying a thin line of paste to the CPU.

The temperatures are cool and consistent across CPUs.

The CPU still starts and stops on that Cineform project though, regardless of whether I'm exporting as a Cineform AVI or as an MP4. I'll get in touch with Cineform and see what I can do about it.

Thanks everyone for your help!