I have the full NI Komplete 10 Ultimate installed, and usually only use a few tracks of soft synths (<10).
With 6 Kontakt pluggins playing, I had 70% system idle.
I was able to run the whole Helena Beat demo song all the way through (with only Logic Pro X open, and Safari with 2 tabs), with around 50% idle system activity.
However, when I tried it with Xcode open, it couldn't make it through.
I have a base macbook air 2015 (4GB i5) and it runs Ableton very capably. I am very much considering buying a macbook with the m7, would I notice much between them? I'm just in love with that screen...