Cheers for the detailed reply Kush, appreciate that
Yep I'm with you on the "number" of antennae, it'll mostly be used with N stuff apart from my pixel and the girlfriend's 6S which are both AC but i'm looking to future proof rather than get insane speeds on our phones.
Not too fussed about guest networks, not sure I'll even need to use that feature at all, but if I do then it'll be 1 at max.
So, I think I'll be better off with the AC, I suspect firmware / feature wise they'll both be the same, VPN is the main "advanced" feature I'd use to connect up from work or my mobile if need be.
EDIT: Tried to rep you for that post but apparently I've already given you too much! Haha.