Finishing PhD early and becoming my PI's postdoc instead
Regarding potential downsides for you:

"Time since obtaining the PhD" is often taken as the academic age, so by graduating early, you make yourself appear older. This can have a formal impact, for example, many grants meant for postdocs come with age restrictions, so are only available in the first n years after obtaining your PhD. 

[Side note: This wouldn't matter for you if you get a faculty position straight away, but at least in my area, this would be quite unusual.]

The academic age can also play a role informally if people have to judge your productivity. (Number of papers)/(Years since PhD) is a formula I've seen a few times in this context.