Uhhh, ZZ+ZBLL.... hmmm, sub-5 average with that method would be tough.
REALLLLYYYY TOUGH.
I was thinking the lower bound to be 7 or 8.
Also, Tomk, you have no idea how ZBLL is recognized, do you?
I mean, looking at an OLL case, and then 4 stickers is really hard. D:
Or even recognizing edge cycles!
That's as hard as determining a U, Z, H perm, and knowing if it's clockwise or counter-clockwise! D:
ZZ+ZBLL is a really good method.
It just needs someone to be good at it, I'm not exaggerating when I say that 40-50 move solves can be achieved on average.