I think that, as long as the framerate doesn't dip below 30, a regular human won't notice fluctuating FPS.

This is complete bullshit, 30 fps is playable for most games, and I have in the past bumper graphics until fps dip to 30/45 because depending on the game 30 fps on high is a better experience than 60 on low for me. But to say that a regular human won't notice it is bullshit. There's a game I play on my deck, for some reason it's very sensitive to disk usage, so if I'm downloading stuff it dips to 30, and I always have to go and stop the download, because if you've been playing at 60, 30 feels very sluggish.