My company does some embedded work. The problem with your analogy is that edge-cases drive CPU purchase decisions far more often than you would normally think.

A simple example: You have designed an ATM using a lower powered ARM CPU. 99.9% of the use-cases never tax the CPU beyond 30%. However, in specific cases where the ATM must simultaneously access the bill dispenser, printer, and note acceptor the hardware interrupts overwhelm the CPU and leads to 2-3 secs of "CPU lock". After those 3 secs, everything returns to normal.

The problem is that the bill dispenser protocol only allows for 1000ms in delay in ack to messages, thus when this situation occurs, the lag is longer than the protocol allows, so it errors out and FUBARs the entire transaction.

In this case, even though this only occurs .1% of the time, the existence of this edge-case will mandate that you not use this specific CPU.

Spoken another way: The ongoing issue of certain edge-cases will cost much more in the long term, than the extra $50 for a different CPU.