The ASUS RT-AC88U was tested using our Version 8 Wireless test process with 126.96.36.199.380_838 firmware loaded. Our standard practice centers the router's antennas on the turntable, both front-to-back and side-to-side in the chamber. This method is intended to keep maximum distance between the router under test and chamber antennas as the router rotates during test. All eight antennas were pointed straight up for testing.
I filtered the charts to show 2.4 and 5 GHz down and uplink profile benchmarks for all 4x4 router classes, i.e. AC2350, AC2600, AC3100 and AC5300. The plots show total average throughput for all measurements.
2.4 GHz average throughput comparison - all 4x4 router classes
Keep in mind these results are with AC1900 class (3x3) client with 20 MHz bandwidth mode used in 2.4 GHz. Note that higher router class doesn't necessarily mean higher performance, even with our 3x3 test client.
5 GHz average throughput comparison - all 4x4 router classes
For a more detailed look at wireless performance using throughput vs. attenuation plots, let's compare the AC5300 with the only other Broadcom-based 4x4 product tested so far, NETGEAR's R8500. I also included the ASUS RT-AC88U since it has basically the same radios, but only one 5 GHz.
For 2.4 GHz downlink, the NETGEAR starts out with the highest throughput, but moves below the two ASUSes from 36 dB attenuation onward. The two ASUS routers track pretty closely.
2.4 GHz Downlink Throughput vs. Attenuation
For 2.4 GHz Uplink, the AC88U and R8500 both start out significantly above the AC5300. But from the mid 20's onward, the three track pretty closely.
2.4 GHz Uplink Throughput vs. Attenuation
5 GHz downlink has the AC88U tracking below the AC5300 and R8500, which track pretty closely.
5 GHz Downlink Throughput vs. Attenuation
For 5 GHz uplink, the AC5300 finally wins one!
5 GHz Uplink Throughput vs. Attenuation
Aside from strong signal 2.4 GHz, these three routers seem to have very similar performance.