Really, that seems a bit excessive. I'd think anything over 20 uncrackable by brute force provided you utilized all character types (alphanumeric and punctuation).
I've got a couple of 1000 character passwords :shrug:.
... I always find it funny that some of my weakest passwords (from a brute-force standpoint) are for my financial stuff, since those sites limit me to 20 characters 
My bank has no such silly restrictions :happy:.
