Why not just replace the TIM with liquid metal? Like a $10 investment and a 15 minute job. Search for it on YouTube, there's people all over getting >15c drops.

There's ways to mitigate LM shorting things out if that's what your worried about.

 

While LM helps a lot, it does not stop thermal throttling, especially since I have the fastest, power-hungry CPU that was available at the time of purchase (4980HQ).

There are indeed ways to mitigate the risks, but apparently LM has to be reapplied after a while and stains the heatsink.

 

If dropping >15c isn't going to fix your thermal throttling, I have a hard time seeing how copper shims are going to help either.

But if the gaps between the surfaces is 0.5 mm or larger, then you should use a pad and not paste.

Make sure you're not buying thermal pads where you should be using thermal adhesive and vice versa. Thermal pads aren't adhesive and need mounting pressure from the heatsink/shim to stay put.

 

I'd probably just use thermal tape of an appropriate thickness. The thing is finding the appropriate thickness.

 

Heatsink the case

I have put .5mm copper shims and 1mm thermal pad across the entire heat pipe and heat sink as you have illustrated. **THIS WAS A PROBLEM** The bottom of the MBP gets so hot it will burn you. I assume that the heat sink is doing such a good job that the fans aren't activating, however low temps for a processor are high temps for human touch. I would like to alter my design to only putting the shims and pads over the heat sinks near the fan, giving the cpu and heat pipe to build enough heat to activate the fans. Did you not have this issue?

 

https://volta.garymathews.com

Try this guys app out and undervolt your CPU, i put a -55mV undervolt on mine, and I disable turbo boost when i know I'm gonna pin my CPU.

I have an early 2015 macbook pro, 3.1ghz which turbo's to 3.4 so not much gained from turboing, my cinebench score has a 12 point difference from no turbo and turbo..

Also, Apple's fan profiles are idiotic.. you need a fan control app, I use the one built into istat.

Attached screenshots.
note that with turbo I had to pin the fans at max 6200 rpm, and it still crept to 102degrees C most of the time.
At no turbo it was more reasonable and I could keep the fans at around 5k which has a more pleasant sound..