While all this has been going on, I played with a 1DX III. Amazing camera. But, on the last day I had it, I transferred 1,000 images, then immediately took out my CFExpress card. I was actually shocked at its temperature...I would call it very warm.
These things do get hot. And I would prefer a camera that will stand the test of time.
Yep they do. But they also cool quite quickly if not being used. I think even ejecting but leaving in the camera will cool it down rapidly. Given the buffer in the 1DX, albeit with smaller images, you may find mild throttling if it gets too hot. Certainly the Delkin do this once the card reaches 86 degrees iirc (might be 88).
As for the heat trapped inside the camera, well that's a different story....