Not a KDE user myself nor Arch. So can’t comment how that might work for you.
I wrote a while ago about how I “modeled” FW12 performance to help figure out how it might work for me. I used a memory/CPU challenged VERY basic (read cheap) ASUS laptop with an older version i3 CPU. You can see that here: FW 12" Laptop Questions - #7 by RodC Maybe you can clean some useful info from it that will help with your decision.
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Rod