Although I’m slightly shorter than you I have pretty much the same requirements, especially as I like short stems and them need a minimum TT length of 620mm
I was hoping to find a hardtail with a -50mm BB as there would still be enough ground clearance and it would give a low centre of gravity and plenty of standover.
Most large frames are too tall for my liking and the lack of standover interferes with steep technical descents and jumps etc.
I’m still making a shortlist, but currently I’m very tempted by the Sunn Tzar, based mainly on it’s length versus height – it’s also made of steel which although is slightly heavy it does flex more than aluminium and should last forever.
I do have a requirement of seat post being >= 30.9 for compatability with my existing adjustable seatposts … I hate 27.2’s, if you want some flex get a suspension seatpost.