At 2.0 GHz, the Pi 400 got up above 60 C and showed signs of continuing to warm up even after 50 minutes, but it was nowhere near throttling. So I tried 2.2 GHz, at which speed the CPU refused to boot entirely. Backing down to 2.15 GHz, it ran just fine, so I left it for three hours. It settled in at a cozy 62.5 C, which is warm, but well within specs.

I ran the CM4 with the larger heatsink at 1.8 GHz to give some basis for comparison to the cheap heatsinks. What a big difference a big hunk of aluminum makes! It settled in at a comfortable 68 C or so. Even pushing it up to 2.15 GHz and leaving it for a couple hours, it stayed just a hair below 70 C — a safe margin on the throttling threshold — and only a few degrees warmer than that huge heat spreader in the Pi 400.

For short-haul links around the financial centers in New York, though, dedicated network links are favored for low-latency connections. Rather than trusting their trades to the vagaries of the Internet and risk an unfavorable routing path or a cable severed by an errant backhoe, high-frequency trading firms often rely on microwave links to exchange information. [...] As it turns out, those microwave connections are the weak link in the system. During the early July heatwave, the links were experiencing slight delays in transmission times over that 16-mile path and throwing off the timing of the trading algorithms. The delay was minuscule — on the order of 10 microseconds — but in a business where millions are made and lost in seconds, that’s substantial.