Is anyone using these for wireless remote gaming either using a Shield or Steam? I know the quality of the experience can vary on a lot of factors such as distance, amount of walls, other devices etc but in general is the experience better than your previous router?
Thats a loaded gun question which will have varying answers.
If i compare the Netgear D6400 to my prior ECI modem and Homehub 3 router setup then yes of course wifi is better on the Netgear.
If someone was previously using equipment of a similar spec to the Netgear though and not just N rated gear then it may be another story.
5Ghz AC also as im glad you realise can vary greatly home to home, due to it being a narrower focused radio wave. It is actually technically possible for someone with a thick breeze block wall to have better performance than someone with a thin Plasterboard wall. (narrow beams like as much free air as they can get in a very narrow path, breezeblock is hollow, plasterboard is not). Its the opposite for 2.4Ghz and N rating that is a wider radio wave.
Asking that question is like asking someone who is a 34inch waist how a pair of trousers fit when you are a 28 inch waist. Pointless to a degree and will tell you nothing about how well the trousers will perform for you.
The best thing you can do is go here.....
http://www.smallnetbuilder.com/tools/charts/router/view
Look up your current gear if it is listed, make notes of wifi figures......
Then lokk up and compare it to the Netgear R6250 on that list
That is basically the same as the D6400 (well as close as it gets, wifi chipset is the same) in this thread only minus the modem and usb port config is different. The rest of the device is very similar. That will give you more of an idea of how well or not it will perform for you as on that site the devices are all tested under the same roof rather than random house designs with people using random wifi receivers.