4K: option to revert back to 1080p on Macbook Retina? I've got a 2012 Macbook Retina talking to a Samsung 4k TV.

I'd actually like to revert back to 1080p.

All the google searches I try talk about going to 4k, but I actually want to go the other way, back down to 1080p.

Although I do get the font-size option to make the fonts larger, it's still only 30 hertz, and it's SUPER choppy when I do screen mirroring.  Also I'm seeing actual rendering bugs.

I bought the TV because it was large, not because it was 4k.  I've used MacBooks with 1080p TVs for years and generally like it.
You should be able to do this with SwitchResX. It'll let you select whatever resolution you choose, and let's you disable HiDPI mode (scaling).