I did some iperf3 tests to look at wireless performance...
The setup is...I've already flashed one AX53U to OpenWrt, while leaving the other as stock (updated to the latest ASUSWRT release). I then configured the OpenWrt one as a wireless client and connected to LAN port (to desktop PC). The ASUSWRT one is configured as a dumb access point.
I ran iperf3 with 4 streams for 60 seconds...
Client (OpenWrt) and AP (ASUSWRT)
2.4Ghz AX
=> 248 to 269 Mbit/s
=> 310 to 335 Mbit/s (Reverse Mode)
5Ghz AX
=> 382 to 442 Mbit/s
=> 501 to 583 Mbit/s (Reverse Mode)
I then flashed the 2nd one to OpenWrt..Then tested again...
Client (OpenWrt) and AP (OpenWrt)
2.4Ghz AX
=> 319 to 348 Mbit/s
=> 366 to 368 Mbit/s (Reverse Mode)
5Ghz AX
=> 377 to 411 Mbit/s
=> 496 to 553 Mbit/s (Reverse Mode)
It looks like the ASUSWRT is slightly faster on 5GHz band, while slower on 2.4GHz.
Out of curiosity, I tested my old AP setup (TP-Link Archer C5) against the new one (RT-AX53U). All using OpenWrt.
Client = RT-AX53U (AX1800)
AP = Archer C5 (AC1200)
2.4GHz
1 Stream => 100 Mbit/s
28 Streams => 116 Mbit/s
5GHz
1 Stream => 253 Mbit/s
28 Streams => 287 Mbit/s
VS
Client = RT-AX53U (AX1800)
AP = RT-AX53U (AX1800)
2.4GHz
1 Stream => 198 Mbit/s
28 Streams => 289 Mbit/s
5GHz
1 Stream => 279 Mbit/s
28 Streams => 430 Mbit/s
I used 28 streams because that is the limit of the Archer C5. The AX53U can handle up to 32 streams. (Each stream is about 14 to 18 Mbit/s).
Another interesting "quirk" I've noticed with the stock ASUSWRT firmware while testing; regarding wireless performance...
Sometimes it suddenly drops speed or stops for a second, but then regains speed moments later. (It looks like some feature in the stock firmware is causing this).
I'm not the only one experiencing this behaviour, this review article indicates the same...
=> https://www.mbreviews.com/asus-rt-ax53u-wifi-6-router-review/
(They have a chart showing their tests for an hour, and there are sudden dips in wireless performance.)
This behaviour does not happen with OpenWrt firmware. The wireless performance remains consistent. No drops in speed when I ran iperf3 for over an hour.
Finally...with the stock firmware, NAT Acceleration is enabled by default. With OpenWrt, be sure to enable Software flow offloading and Hardware flow offloading. (All tests had these enabled by default).
...Think I'll test wired performance next. (NAT, Software/Hardware flow offloading on and off, etc)