Oldest kindle model able to run Koreader?

I’m currently using a very old kindle gen 4th and honestly it works fine and I’d keep using it, if it weren’t because koreader is extremely laggy and buggy (it keeps refreshing into kindles home page). I figure this is due to how old the kindle is that it can’t keep up with it.

So I’m thinking of buying a used old kindle model that,however, could be able to run koreader fine. I know performance won’t be top notch compared to the newest, of course, but I’ll be happy by getting it to work just decently enough where it’s not almost crashing every minute.

I’d like also a better screen since I discovered you can read mangas with a koreader plugin, but that’s just an extra that I could live without.

So, what’s the oldest model you’ve seen koreader work fine without crazy stuttering or lag?