Unfortunately "Marketing ploys, and Drama Queening" took over technological fair discussions during the passing 5 years.
Mimo per-se and Dual band are existing for a while.
The theoretical addition of 802.11ac over 802.11 a/b/g/n is not really translated to any significant improvement in real life functional Wireless Networks.
I have both the Asus N66U.
http://www.newegg.com/Product/Produc...82E16833320091
And the Asus AC66U
http://www.newegg.com/Product/Produc...82E16833320115
I am sure that if I'll spend some time with the Tech Data I'll find some convoluted experimental way to show some gain while using the AC66U.
In real mainstream use of the two I can not find any real performance difference.
That is good for you. I get exceptional performance out of my N600 router and Intel 7260ac card in my laptop. Around 200Mbps same room 5GHz performance and 180Mbps same room 2.4GHz performance. 5Ghz drops off rapidly to the point where 2.4GHz is easily faster just one room over.
I have pretty good coverage.
Enter the AC1750 router I am using. With 5GHz with that same Wifi card, I get 420-430Mbps same room 5GHz performance. That is...uh...more than double the speed.
Even a couple of rooms over, the performance is still very strong, up around 200-350Mbps, well over the performance I could get on 2.4GHz.
The router is faster on 2.4GHz as well over my N600, about 220Mbps, but 5GHz is faster until you are pushing the edges of 5GHz reception, at which point 2.4GHz ends up being a little faster, and then you lose the 5GHz signal and 2.4GHz is of course much faster and stretches a lot further.
Testing a bunch of locations through my house, disabling my access point, I see a gain from about 115% down to around 60% on 5GHz (just 5GHz vs 5GHz, not 5Ghz vs 2.4GHz). Figuring what 2.4GHz could do (so factoring in some 5GHz AC versus 2.4Ghz N performance), versus 5GHz, etc, etc, I come up with around an average normalized 35% gain through out my house. Of course the new router is a little faster on 2.4GHz too (yay beamforming or some other improvements) and it ends up being more like 50% faster averaged through my house.
In the rooms where I am most likely to be actively using wifi and/or where I am going to need/want the most performance (IE file transfers, and not just video chat, internet browsing, streaming audio/video) its more like 80% average speed increase.
Downside is, the router doesn't provide great coverage over my whole house, so on goes the 11n N600 AP. If I were to replace it with the same router in AP mode, average gain would probably be closer to 80% whole house averaged.
So...yeah. 11ac. Complete garbage. Wish they didn't invent it at all.