Performance - more
The 5 GHz downlink plot shows very similar throughput at attenuation levels up to 18 dB, where the plot lines diverge. The AC56 takes a premature dive toward the bottom. But it recovers to end up with the best range performance, i.e. still producing 34 Mbps throughput at 45 dB attenuation.
5 GHz downlink - Throughput vs. Attenuation
The 5 GHz uplink plot shows the AC56 with some wonkiness again in the mid- 20 dB range and a dip in the early going, too. But it once again bounces back to a much higher throughput. At 39 dB, however, it is pretty much out of gas. I don't know that I would trust that blip up at 42 dB to provide consistently superior range.
Again, note the significantly reduced scale with uplink throughput values around half of downlink.
5 GHz uplink - Throughput vs. Attenuation
Since the top-ranked ASUS USB-AC56 is more than twice as expensive as the second-ranked Edimax EW-7822UAC, let's quickly compare their profile plots.
ASUS USB-AC56 vs. Edimax EW-7822UAC Profiles
The two are pretty well matched for 2.4 GHz performance, with the Edimax, in fact, outperforming the ASUS on downlink. In the 5 GHz band, however, both adapters have their oddities. On downlink, both take downward throughput dips, then recover, with the ASUS turning in better overall average throughput and range. But on uplink, it's a hard call; both have some pretty severe mid-range issues.
For the most part, the ASUS USB-AC56 turned in the best overall performance to earn its first-place ranking. But the adapter might not be the one for you. First, at $70, it's the most expensive of the bunch. But the large external antenna would be more of a problem for anyone planning to use this on any device that moves around. This product really seems more suited for use with desktop computers, media players or anything else needing wireless network connection that isn't going to be moved much.
Although I'm as surprised as you may be to see the least expensive product in this roundup perform almost as well as the best, the Edimax EW-7822UAC seems like it could be the best buy of the bunch. And if you are looking for an AC adapter for your Linux or MacOS machine, it's the only one that ticks that box.