Used T4xx-series Thinkpad is what I'd go for. Maybe with an SSD and RAM upgrade.
FWIW, the biggest resource drain for me these days is modern web browsers. My 2013 Air is stlll usable but I can only have one Firefox session running and then I need to periodically kill and restart it to shrink the memory footprint.
Compared to that, my devtools are perfectly zippy; mruby rebuilds from scratch in about 30 seconds.
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