I've been having nothing but problems with Asus's PCE-AC66 wireless card on my rig; and their support didn't help all that well.
A few things; I have some random linksys router across the house and my primary router is a netgear WNR-1000 v2 (rented from comcast; the one i use for the PCE-AC66)
I've also tested other methods of connecting wirelessly to the router; I've used a wireless-g "WifiMAX" usb adapter and works flawlessly on both routers; and usb tethering with various android phones works fine as well.
I had previously sent this card to ASUS RMA because it kept locking up and crashing my desktop (even after troubleshooting with tech support) and just got it back today; it no longer locks up my system (yet.) but still has the problem of an extremely lossy connection to the router regardless if there are any interfering APs or not.
I literally can't even browse the web without running at dialup speeds or just have the connection dropped totally (even if it says its still connected to the internet) while all other methods are working out just fine.
System Specs
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Mobo: Asus Sabertooth 990FX Rev 2.0
Mem: 16GB PNY Optima 1366mhz (overclocked ~1.4ghz stable)
Cpu: AMD FX-8150 (overclocked 4.12ghz stable)
Gpu: XFX Radeon HD 6870 1GB
PSU: Thermaltake "Blackwidow" 850 Watt
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I don't know if these issues are just because of the router so i'm holding off on going out to get a wireless AC router for the moment.
-NH
Update: Seems to have resolved itself for the moment, after a lot of tinkering, restarting, and tossing out the AC-66 Wlan utility to just use the windows wireless manager, it seems to run fine thus far. getting stable pings on Diablo III (125 ish) and BF3 (under 100)
Will update if any extra issues arise