Ok, not sure why mine measured smaller, but I even remeasured around in multiple locations I still got about 4.37 +- .03mm so I called it what I found rounding up to the nearest .1mm. I guess measuring with digital calipers is not the most accurate way, using a set of numbered drill bits to check diamter would probalby be better.

Anyhow, the second from the smallest...

I'll give a couple of sizes a try and see if my single D5 has a different preference. I would also think quads may favor a slightly larger nozzle as it becomes less important to cool right in the very center and more important to cool the whole base well.