There's exactly one threshold which produces a binding outcome:
3(a).vSo yes, 50%+1 is indeed the standard to set in motion a mandatory leadership election process.
At every convention that is not a leadership convention; a secret ballot vote will be held to determine whether or not a leadership election should be called. If 50% plus one delegate supports the calling of a leadership election, such an election will be held within one year of the convention vote.
In contrast, any other threshold being thrown around within the pundit class is simply a matter of judgment. Any leader has the discretion to step down at any time - and talk of 70% or any other number represents pure speculation as to whether Mulcair might choose to resign his post, even though he's won in terms of the formal requirement to stay on without further review. And whatever numbers anybody else throws out, we wouldn't necessarily expect a matter of personal judgment - as distinct from voting process - to be defined in advance.
At the same time, nothing in the NDP's process suggests that a leader could lose on a majority vote, but deny the vote has any significance after the fact by claiming uncertainty about voters' intentions. Because that would just be asinine.