>> How many http requests do you need before you have to switch to any of these?

Or how many metric tons of CO2 do you want to produce before switch to any of these. You see performance is an interesting problem.

This is a non-issue for literally 99.99% of applications and considering it before being "at scale" is simply a waste of mental energy.

You are missing the point.

As somebody pointed out there are millions of applications that can use Rails because scale is not a problem for them. If all those millions of applications do 1 req/s then you have 1M req/s served with Rails instead of something that is more reasonable. The CO2 production of these low scale Rails web app quickly add up.

How comes this? A higher CPU consumption currently it is going to have a higher CO2 footprint, even in a cloud-based, shared-VMs scenario.