Just a note that I personally have no more major issues with the WRT1900AC(S) family -- the last issue I had (bi-directional speed on 5G) seems to have been mostly addressed with recent commits in LEDE source.
iperf3 -c <target ip> -P6 -t20 yields (ACS to AC, both on LEDE):
[SUM] 0.00-20.00 sec 934 MBytes 392 Mbits/sec 826 sender
[SUM] 0.00-20.00 sec 930 MBytes 390 Mbits/sec receiver
iperf3 -c <target ip> -R -P6 -t20 yields:
[SUM] 0.00-20.00 sec 287 MBytes 121 Mbits/sec 23 sender
[SUM] 0.00-20.00 sec 287 MBytes 120 Mbits/sec receiver
The result here is the same if I run the server on the ACS and don't use -R -- that direction is always slower but I may see rates around 200 Mbits/sec.
File transfer from AC to ACS: ~25MB/s
File transfer from ACS to AC: 28-32 MB/s, averaging ~30MB/s
uptime
20:39:11 up 2 days, 1:55, 0 users, load average: 0.13, 0.08, 0.03
For some reason there's still an imbalance in iperf but significantly less imbalance with file transfers and the typical slowdown after a day or so has not (yet) occurred.
I remember lockups that happened after 4-5 days in the past and those are behind us -- hopefully the slowdowns are as well. Unless a major reason to rebuild comes up I'm going to once again attempt the long-term stability test.
Maybe now is the time to complain that with stock firmware in the AC as a bridge I'd get better than 40 MB/sec transfer rates... gotta keep the dream alive.