As noted in the opening, the EA9500 is the first 4x4 Broadcom router to support MU-MIMO in official factory firmware. Linksys does provide a caveat that only two MU-MIMO clients are supported per radio, however. Since MU-MIMO routers don't just stop supporting MU-MIMO devices as more are added (as our tests show), this is an odd statement. But I take it to mean the EA9500's MU-MIMO is a work in progress and will be improved with a future firmware update.
Linksys was kind enough to provide four of its WUSB6100M Max-stream AC600 Wi-Fi Micro USB Adapters for MU-MIMO testing. But they're still in the box. I instead ran our standard MU-MIMO test process using the Ixia Veriwave system. The Veriwave requires cabled connection to the router under test's radios, so I had to pop the top and use pigtails to connect to the teenier-tinier IPEX MHF4 connector that seems to have replaced the just plain tiny U.fl antenna connector. I lucked out with the more accessible placement of the 5 GHz low-band radio's connectors and didn't have to remove a heatsink plate to get at them.
Since the EA9500 is a 4x4 MU-MIMO router, it's fair to compare it to other 4x4 routers with working MU-MIMO, most of which are AC2600 class. I know I repeat myself, but there are no other AC3100 class or AC5300 class routers that support MU-MIMO.
It's also worth noting the Veriwave emulates standard 1x1 MU-MIMO STAs with 433 Mbps maximum link rates vs. the 866.7 Mbps the EA9500 is allegedly capable of using 1x1 1024 QAM. But since the same STA is used on all products, it's a fair comparison.
I decided to let the chart include the 3x3 Linksys EA7500 MU-MIMO router, mainly because it beats the 4x4 EA9500. The odd-duck AC2200 class ZyXEL NBG6815 is fairly included because it has a 4x4 5 GHz radio.
With all that said, the EA9500's average MU-MIMO throughput of 319 Mbps places it third up from the bottom of the chart.
MU-MIMO Average Throughput comparison
SU (single user) MIMO tests show how efficent routers are at serving multiple STAs. Ideally, total throughput should be divided among active STAs, with none lost. This benchmark is also good for showing MU-MIMO routers that are likely to misbehave when dealing with multiple non MU-MIMO clients. Although the EA9500 is on the low side, its 313 Mbps average throughput doesn't indicate trouble as bad as the ZyXEL and TP-LINK Archer C2600's numbers do.
SU-MIMO Average Throughput comparison
The MU, SU Throughput Difference lets you quickly zero in on products with better MU-MIMO throughput gain. The EA9500's result of 6 means it doesn't provide much more throughput with the 16 STAs used in the test than a non MU-MIMO router would.
Average MU, SU Throughput difference
The MU, SU Difference vs. STA plot can get messy. So I just included the QCA based Linksys EA8500 for comparison. The EA8500's plot shows peak throughput gain of 370 Mbps with six STAs. The EA9500's throughput gain peaks at only 151 Mbps with three STAs, then falls off rapidly to move to a throughput loss from 7 STAs up.
MU, SU Throughput difference
The SU-only comparison shows the problem isn't with SU throughput, which has the gradual decline typically seen. The main problem is MU performance, which, as Linksys knows, still needs more work.
SU Throughput vs. STA
I apologize for not testing Smart Connect performance for the EA9500. The new test processes take a lot more time and with the retesting required to provide comparison products for the charts, I'm having to make hard choices about what not to test. Fear not, band-steering and load balancing testing is still on the radar. I just need to make it more automatic than the manual process I've been using.
At any rate, the testing I have done shows the EA9500's wireless performance very similar to last year's crop of AC5300 routers. The EA9500's main differentiation at this point, aside from the lets-keep-em-confused AC5400 moniker, is its lone-wolf status as a Broadcom-based router that has working MU-MIMO. In the end, this is just another really expensive router that's unlikely to light up any of your pesky dead spots or handle a large number of devices any better than a much cheaper AC3200 class tri-radio alternative.