Saw an anecdotal comment about arm64 being more efficient for weak references (more efficient than strong) so this may only be anecdotally imperceptible. It would make for an interesting blog post to compare the assembly between accessing a strong outlet and a weak one.

This post talks about class pointers containing info on weak references.
http://mjtsai.com/blog/2013/09/24/ios-on-arm64-has-inline-retain-count-in-the-isa/

To be honest, I've seen the use of weak outlet references resolve retain cycles, but I don't recall in which era this was. (iOS 5 or iOS 6).