Tested my environment with two different laptops and the same result. Flashed back to .29 with 0 configuration changes and speeds are back to what they were. Flashed back to .30 and have the same slow speeds. Cleared NVRAM. Same result. I don't make it a habit of randomly changing configs when I update firmware because I want to see if there is any performance differences. Maybe you should check your build.
Works fine here. RT-AC66U in a room, and laptop in another room. Wireless card link speed at 270-300 Mbits.
Anyone else with positive or negative performance on the RT-AC66U wireless?