I upgraded my Asus AC66U for the R7000 a few weeks ago and really like it. One problem I noticed today is with my Chromecast. I am using it on a 2.4Ghz network and it will not connect if I have the mode setting on 600 mbps but it works fine on the 289 mbps setting. Anyone else noticed this? I filed a bug with Google. I am running with ip6v disabled.
I also upgraded from an AC66U and I use my two chromecasts with my R7000 set to 600mpbs. I didn't have a problem connecting but I didn't seem to get the faster speeds until I turned WMM QoS.
BTW. My AC66U makes for a nice bridge with the R7000 with speeds of 1300mpbs