I use Xbox 360s as WMC extenders and I want to remove congestion on the n band for the one I don't have using a power line network adapter. I will eventually wire up my home with CAT6 when I get the time.
I still don't understand how AC matters, especially when you could do powerline networking although I'm sure there's a reason you haven't done that already. First, how far away is it from the intended access point? AC might be no better than N. Also, you will need an AC bridge at the XBox as well. How many other devices do you have on N which make you feel it is 'congested'? Does the XBox only have issues when other devices are using the N network? Also, afaik AC uses the same 5GHz frequencies that N does, so if the congestion is from other networks AC won't help.
I was a little annoyed when AC came out and routers and some devices started integrating it not long after I upgraded my early N router. But then I realized AC is limited in range (a lot of the advantage of AC comes from using wider max 160MHz channels in addition to 5GHz), that it would only matter for intranet transfers and then only for fairly large transfers. I decided that having a very good N router was just as good because the only issues I ever have are at the edge of the range which AC won't change.
But if the point is to get teh new shinies, then go for it
Some of the perks of AC:
1) Single Channel Architecture (no more MCA)(meaning with multiple APs, the entire network
looks like one AP, instead of the cell-based MCA we use now)
2) Multi-user MIMO (up to 8 streams)(my cellphone does 2 simultaneous streams)
3) Beamforming (attempts to "steer" the signal towards the recipient)
4) 160MHz wide channels (you *need* to use the wider channels to see the higher data rates)
5) > 1Gbps aggregate
backplane, supporting multiple stations per AP
6) With multiple antennae, channel bonding, and likely multiple radios as well, data rates of up to 6Gbps should be possible (433Mbps at the least)
7) IIRC, they updated the PHY as well
8. You can use the 5GHz channels plus the 2.4 as well, so as you get far enough away from the AP, instead of just losing all signal, the client device will shift to the longer range 2.4
It's true that 5GHz radios have shorter range than 2.4GHz. That's just how it works. The greater the frequency, the shorter the distance. That's why 900MHz signals propagate much further, and why 60GHz WiGig will only have a ~10ft range. Unless you start adding in amplifiers, but that's another story (and also can run afoul of FCC rules).
And you're also correct that the further you get from the radio, the lower the speed will be. That's why even old 802.11b had 4 different data rates, depending on distance. Whenever you see a speed rating for an AP, always
assume the manufacturer is talking about being within spitting distance (and LOS) of the radio. With 802.11n, I think the furthest you could be from the AP, and still get the full speed was 40ft. Not a big deal at home, but it becomes very troublesome in larger installs, like I've done. With .11b, since it was 2.4GHz, you could be 110ft from the radio, and still get 11Mbps.
I should point out that while greater frequency = shorter range, greater frequency also means faster data rates.
And none of the above gets into the issues of antenna selection, since I'm assuming this is about an indoor home install. Home units tend to ship with 2-3db omnis. You'd need the proper ends, crimpers, LMR-400 coax (10ft per run max), and mounting equipment, but you really can 'shape' the signal and buy yourself a little extra distance by using different antennas.