Choosing OS X version for a mid 2011 Macbook Air 4GB As I understand the matter, it is generally better to use a later version, however, I realize that the newer versions are really designed for more powerful hardware.  The MacBookAir4,1 in question is a dual core I5 1.6 Ghz CPU with 4GB of RAM.  It is currently running El Capitan.

The choices include:


Mojave (latest, requires 2012 or later Macbook Air) 
High Sierra
Sierra


What is an appropriate quantitative test to determine which of the three will run on the MacBookAir4,1 with a comparable performance to El Capitan?  While anecdotal reports are fine, any benchmarks to support a position should alleviate the issue of being 'opinion based'.
I have a 2010 iMac and I'm running High Sierra. It has been running smoothly but my machine gets very sluggish sometimes when running Xcode. I can't compare it to El Capitan because it has been too long to recall. It has been as stable as Sierra though. I think the only issues you'd have would be due to having 4 GB of RAM. The size of the system would be very important, I'd think, for a 4 GB machine. I don't know the relative size of your system but there are many apps that will tell you the amount of free RAM you have. iStats, Monity, and SystemPal from the app store are 3 such apps that will display how much RAM you are using and how much is free.