Choosing OS X version for a mid 2011 Macbook Air 4GB
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.