We are not in competition with Manjaro’s KDE edition, they both have their own use cases.
Netrunner rolling uses Netrunner specific settings, patches, and enhancements.
That’s an older xeon proccessor, do you have it overclocked?
What display adaptor/driver are you using with it?
Have you tried using a different kernel series? (4.4.x LTS would probably be best considering the processors age)
Have you tried using pepper-flash (Extra) with freshplayerplugin (AUR)?