Your description matches what I understand about FREQ/AFREQ.
An AFREQ value less than one means that my CPU is running at less than full speed when not in a sleep state. Given that I've got the frequency nailed at 1.8GHz and my OS is not configured to support any of the frequency-varying stuff like cpufreq, t-states, and such, this is highly unexpected.
Or am I missing something and there's another explanation?
Incidentally it's actally lower frequency and worse latency on all non-zero even cores (2, 4, 6, 8, etc) relative to core 0. And also for all non-zero odd cores (3,5,7,etc) relative to core 1. Basically the first hyperthread sibling in each socket seems to be treated specially somehow.