Maybe use the b43 driver?
now 8011n working when change to driver kmod-brcm-wl ,ref the site https://wiki.openwrt.org/toh/asus/rt-n16.
using speediest, ISP speed 100mbps(download)/10mbps(upload), got 52mbps/10mps. when use asus origin firmware got 80mbps/10mbps。
same as openwrt,what the diffrence?