For me, location of the router was key. I was having issues with mine and
after optimizing the channels I moved it from the basement to the first
floor and got 80% there with signal. Then i experimented moving it around
on the first floor (bought a 50ft ethernet cable from Monoprice) until I
got the signal and throughput I wanted. I then spent time running a
hardline through the walls to that location (cat 6e, not using the 50ft
Coincidentally, I'm moving into a new-to-me house this week and will have
to go through this all over again!
I only have N, Linksys N900, so I won't comment on AC.