Bingo.
The damn cooler is so bulky that it made it very hard to see the gap between the GPU and heatsink. I removed one of the little plastic pads and tried it again, worked like a charm. Now running at 36 degrees idle.
A few things I have learned, in case anyone else attempts something similar:
- The instructions are rather bare, look online for videos.
- The components that attach the cooler to the card and top heat sink are confusing, I missed the heatsink gap completely despite following the instructions to the letter.
- The clips for the top heat sink/grille are barbaric, and do not fit this model of card particularly well. It is doable with some patience and a large case, but in my case the card bent slightly no matter how carefully I used the thermal pads and clips.
- The cooling unit works just fine without the top heatsink/grille.
Thanks for the insight 4745454b!