Router / Wireless Stress
I didn't have enough computers to simultaneously run wired routing, all three radios and storage testing. So I dropped one 5 GHz client from this stress test and reassigned two computers to drive wired routing traffic from WAN to LAN. This means the remaining computer connected to the AC87 LAN is streaming traffic to both 2.4 and 5 GHz wireless clients.
The plot below starts the 2.4 GHz radio traffic first. At 20 seconds, WAN > LAN traffic is added, capped at 300 Mbps/sec. Then at the 30 second mark, 5 GHz traffic flow starts. Routing traffic is capped at 300 Mbps so that results can be fairly compared to the R8000's.
The good news is that there appears to be very little interaction between the radios and wired routing. There's only a bit of a downward glitch in routing and 2.4 GHz throughput when the 5 GHz radio kicks up to its maximum throughput level. Total throughput of 857 Mbps is higher than the 765 Mbps obtained in the same test run on the R8000.
The difference is primarily due to the AC87's significantly higher 2.4 GHz throughput, averaging around 275 Mbps. In the same test, the R8000 averaged more like 115 Mbps. I should have mentioned earlier, in both the R8000 and this stress tests, the 2.4 GHz radios were set to 40 MHz mode, to allow for maximum throughput.
ASUS RT-AC87 Stress Test - Router, 2.4 & 5 GHz radios
My last stress test was to check for interaction with USB 3.0 storage. Routers with USB 3.0 ports must take care with internal design and shielding to prevent impairing 2.4 GHz radio performance (and vice-versa) when both are active. ASUS' RT-AC68U is an example of poor USB 3.0 port design. In our retest, the AC68U's USB 3.0 port storage throughput looked the same as USB 2.0 with the Reducing USB 3.0 interference setting disabled.
ASUS moved the USB 3.0 port to a front corner of the AC87 and this design looks successful. In the First Look, I found filecopy performance using the USB 3.0 port was much improved with 50 MB/s writes and almost 70 MB/s reads.
For this test, I used a different computer and test file than used for the First Look Filecopy tests, so results are different. The screenshot below shows a drag-and-drop filecopy of a single 1.15 GB Windows backup file from the computer connected to the AC87's LAN side to a WD Passport USB 3.0 drive shared by the AC87 as an NTFS formatted folder.
Filecopy to USB 3.0 drive - no other activity
The next plot shows the same sequence as the previous plot above, but with the drag-and-drop started 60 seconds into the run. The big dropout on the 5 GHz stream is unrelated to the filecopy test as far as I can tell. The more important result is that 2.4 GHz throughput seems mostly unaffected.
ASUS RT-AC87 Stress Test - Router, 2.4 & 5 GHz radios, with USB 3.0 filecopy
As we saw with the R8000, filecopy throughput is affected, with a ~25% reduction.
Filecopy to USB 3.0 drive - Router, 2.4 & 5 GHz radio traffic
I also ran a test to look at interaction between 2.4 GHz activity and storage filecopy only. The plot below seems to dip a bit during the period where the filecopy is running between 00:30 and ~01:20.
ASUS RT-AC87 Stress Test - 2.4 GHz radio, with USB 3.0 filecopy started @ 30 seconds
Filecopy throughput is again reduced, but not as much as before.
Filecopy to USB 3.0 drive - 2.4 GHz traffic only
My conclusion is that ASUS has done a much better job of controlling USB 3.0 and 2.4 GHz radio interaction than in the RT-AC68U. But there still seems to be some minor interaction between the two.