To those of you screaming at your screen that internet speed test benchmarks are weak-sauce and that I should be smacked for underutilizing such nice hardware: relax, I hear you. The next section isn't super-comprehensive, but it'll hopefully placate those who want to see big numbers.
We need to introduce some new players before we get started. I believe you all know my friend the Samsung 850 EVO. He'll be playing the role of network-attached storage with the support of a StarTech USB 3.0 SATA adapter. You may also be familiar with the Asus Zenbook UX305. I used the older Broadwell model and its included USB 3.0 Gigabit Ethernet adapter to play catcher for the packets that my trusty Clevo W110ER pitched to it using iPerf.
The Ethernet adapter in my Clevo notebook is a Realtek Gigabit Ethernet chip. The Wi-Fi adapter in my Clevo is an Intel 7260. Keep in mind that it is only a 2x2 solution, so you won't see numbers here where the RT-AC88U and RP-AC68U are really stretching their legs. These tests were performed using the same physical locations and configuration settings that were in place for the internet speed tests. The UX305 was set to airplane mode and used Ethernet for every test. Once again, I used the fastest repeatable result to eliminate outliers and give the benefit of the doubt to environmental conditions.
These tests were run less than ten feet from the equipment with no walls separating the router or extender from my laptop.
Take a little time to read and understand the descriptions of the test associated with each bar in the graph above. They spell out how the hardware was connected for each test. It's worth noting that the Ethernet to Ethernet tests are probably underperforming because of the USB adapter or the Realtek controller in my Clevo. That said, you can see that the test setup is at least capable of anything up to those speeds.
The real standout number is the scary looking 3.18 Mbps result from when I was connected to the extender with Wi-Fi while the UX305 was plugged into one of the extender's Ethernet ports. I've been in touch with Asus about this result and its techs tried to replicate it without success. It's possible that it's a problem specific to my test setup, but keep it in mind if that crazy scenario is something you might duplicate someday.
Another number worth pointing out is the 152-Mbps result from the Ethernet-connected router-to-extender test. That result matches up nicely with the link rate that the extender reports itself. Other than that, it seems like when the extender is first in line or Wi-Fi is involved the transfer speeds at range aren't all that much faster than the internet connection. That feels like evidence that I've achieved my goal of maximizing the highest-speed internet connectivity possible across the largest range possible.
Next up we have some results from CrystalDiskMark using the Samsung 850 EVO and the Startech USB adapter. What we're looking for here is what kind of transfer rates you can expect from using the RT-AC88U and RP-AC68U for NAS duties under various scenarios.
For comparison I've included both the native SATA 6Gbps results and the results of the 850 EVO hooked up to my Clevo's USB 3.0 port. You can see that adapter does a fairly decent job of keeping up with a native SATA port. You can also clearly see that the NAS performance of the router is nowhere near the limit of the drive. That's not unexpected, though—these sorts of features are not headliners and not many folks would use an SSD as a router's NAS drive anyway. That's not to mention that 1Gbps works out to 125 MB/s. A more traditional mechanical drive would be more appropriate here. (I can't believe I just wrote that.) My standard disclaimer about prioritizing range over speed aside, performance from attached storage seems perfectly respectable, especially if you have an Ethernet connection to the router.
The eagle-eyed gerbils among you may have noticed that some logical tests are missing from the graphs above. You're not wrong—there should be four additional tests where the USB adapter and 850 EVO are plugged into the RP-AC68U extender instead of the RT-AC88U router. I tried to test that combination but ran into a problem where the network share would only show up as having 3MB of space on it after configuration. That's not enough to run benchmarks.
The same drive with the same settings shows up with all 500GB when it's connected to the router instead of the extender. I covered the basics when it came to troubleshooting this issue: restarting the extender, making new volumes on the drive, and confirming that all devices had the latest firmware. I reached out to Asus for help and its techs haven't been able to replicate this problem, either, so again, it could be specific to my setup.