I think you are going to have to experiment. (The N3 has few WiFi controls in the stock UI, so I would concentrate on the router settings.)
Your router allows you to logically separate the two radio bands (see manual pg 34) into distinct networks with different SSIDs, and then toggles to control individual protocols e.g. g/n/ac and/or "mixed" vs single modes in each logical network/band.
So I would experiment with those... and perhaps even go so far as to turn off all your other devices to see if they are affecting your measurements. Not that you would operate that way, but it might provide you with a few more clues.
"I'm gonna start coding placebo apps. That way I will be sure that the complaints are real and the praises hollow."