I’d been running two 4K monitors off my MacBook Pro and noticed high cpu usage and a non stop fan in the afternoons when the room got a little warmer. Turns out the integrated gpu is struggling and the cpu spends more cycles handling cooling management.

This got annoying enough that I invested in an external gpu (not cheap!!) which resolved my issues. I get it — 4K and 5K monitors require much more graphics processing and a MacBooks integrated gpu can only do so much.