So you took the plunge to get a good router instead of a flaky $40 plastic box of crap. Good choice. But if you use a wireless bridge then you probably should be aware of the following problem and fix.
There are numerous huge gaping security holes in the older (and possibly, depending on when you bought it, STOCK version) of the firmware on the routers. Now luckily Asus has patched those holes (download the latest firmware on the Asus website, as the auto-updater is a bit flaky on finding the very latest version). However, the latest patched firmware makes media bridge mode an exercise in frustration. The bridge mode Asus RT-AC66U will be very flaky. Usually in about a day it stops issuing new DHCP leases and doesn't renew DHCP leases when they are requested. But clients with an existing good lease will still route correctly. Eventually DNS will stop resolving properly and that expensive router becomes a well designed paperweight. The solution is to keep the wireless router on the most recent firmware, but to keep the media bridge on firmware version: 184.108.40.206.374_726 Note that this means your router is vulnerable to attack from those connected into it ... but somebody physically wired in to your media bridge probably has more delicious (and worthwhile) things to exploit than your media bridge.
For those wondering if third party firmwares will solve this bug, I have tried RMerlin's firmwares and they seem to suffer from the same issue. Deep deep Googling around suggests there is an actual defect in the chipset inside the Asus RT-AC66U causing the blaky bridge performance which requires detailed attention in firmware to mitigate.
Hope this helps people like me who depend upon media bridge mode on the Asus RT-AC66U but want at least their primary router to not be a gaping security hole.