> I was able to work around most of the cooling-related issues by mounting the laptop vertically...

Have you happened to measure the thermal difference vertically mounting your laptop? I also vertically mounted my home server laptop for the same reasons, but noticed the fans seemed much louder so I returned it to be horizontal like normal. It's as if they were designed so that the horizontal surface acts to attenuate their high-frequency sounds. It's still annoying, but less so. I'm wondering if going vertical again, but throttling the CPU as you've done is the way to go.