This is a small suggestion, as CircleCI 2.0 went towards GA, we noticed we have more and more misses on cached docker images.
As we are a small team of ~10 devs, but push frequently, about 70-80 builds a day (with 3 nodes on each build), having a more limited number of servers our code would run on would greately improve build speed. For us, biggest bootleneck seems to be pulling 4-5 docker images when we hit a server that has no cache of the docker images.
From what I saw, starting the build takes from 10sec to 80 seconds depending on if we are on server having the cache or not.
Just an idea