I did some more test with the Netgear Nighthawk R7000 and it is faster then the Asus RT-AC68U.
I can do the 877.7 file in 17.05 second wich is 51.47MB/s !
I saw a peak at 62MB/s in some test !
And it is stronger then the Asus upstairs in my office.
(Got to go thru a concrete floor and a wall)
With the Asus it give me 14 to 16 MB/s upstairs and with the Nighthawk
it run at 24 to 28 MB/s. It's real good !!!
Also I know my way around in the Netgear router parameters and I like the Netgear App "Genie". And I was very happy with the R6300 it was the best router I had, very strong and stable !
So I'm gone keep the Nighthawk and return the Asus.
I think If I don't find the problem with windows-7 wifi AC I will have to get use to Windows-8.1...
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