Best estimates on 3.x LTS for new project work

Depends on what you mean by support. v3 will be used for years (if not a decade+) after v4 comes out. So there will be a user base and, honestly, its just PHP, so if something isn't working or needs changing - you can either extend the core (or if v3 seems to lose all support you need, just change it yourself)

v4 from v3 will be a clean break (from what I gather) where it will be a project to update to v4 and not just a few fixes here and there.

We had that choice for a large project and went w/v3 because v4 is more pre-alpha than something we'd want to put on a live server (we did however, go with an alpha software elsewhere and that bit us in the butt, so... I really don't recommend it)