How do I convert a .mov to GIF in the CLI, with high quality.

I run a website that relies heavily on gifs (for now, switching to newer tech soon) https://musclewiki.org

I'm looking for similar quality/file size to this: https://musclewiki.org/exercises/Abdominals/Crunch-Side-021316.gif

I've been reading online about ffmpeg and imagemagick but every time I get close to that quality, it's about twice the file size.

Can someone help me with a one liner that will convert .mov > GIF (in batch) with reasonable quality? Or at least point me in the right direction. The old way (via a 3rd party website) just isn't scalable as I need to add another 400 videos.

Thanks