I have a Netgear R7500v2 which I used for years and is great working order. I have been looking at changing from the stock firmware finally and have done some testing which leads me to a question.
Here are some results from recent speedtest tests. Note that I have 1GB Fiber Only with ONT from Verizon FIOS.
Stock Firmware - 800-900Mb/s
DD-WRT - 900+ Mb/s
OpenWrt - 500-600 Mb/s
Is there thruput limiting on the WAN port in OpenWrt that I'm not seeing?
What firmware are you using?
ubus call system board will show that.
I have an R7800 with exactly the same problem. (I think both have the same IPQ806x under pinning).
My throughput also diminished from about almost 900 Mb/s running DDWRT to below 600 Mb/s running OpenWRT Kernel 5.15
However as we speak I am testing a patch which dramatically improves my performance to above 800 Mb/s. Maybe this also will work for your R7500v2?
I also have an EA8500 for which I will check the coming days if this patch also will improve throughput.
So there is hope that it will be better 
Currently, I'm on the latest release of DD-WRT for the r7500v2.
When I tested OpenWrt it was this one: https://openwrt.org/releases/22.03/notes-22.03.5
The r7500v2 is ipq8064 based, the older/ slightly slower brother of ipq8065 and the r7800/ nbg6817, everything said about them applies here as well:
And yet I consistently see 800+ Mb/s with other firmware. Just trying to see where the discrepancy is.
It looks like there is long standing bug
Measured between 2 modern multicore PC's running iperf3 one wired on the LAN side the other wired on the WAN side
Router doing nothing else no Wireless.
{
"kernel": "5.15.123",
"hostname": "EA8500",
"system": "ARMv7 Processor rev 0 (v7l)",
"model": "Linksys EA8500 WiFi Router",
"board_name": "linksys,ea8500",
"rootfs_type": "squashfs",
"release": {
"distribution": "OpenWrt",
"version": "23.05-SNAPSHOT",
"revision": "r23314-7efec0acca",
"target": "ipq806x/generic",
"description": "OpenWrt 23.05-SNAPSHOT r23314-7efec0acca"
}
}
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-30.01 sec 1.71 GBytes 490 Mbits/sec sender
[ 4] 0.00-30.01 sec 1.71 GBytes 490 Mbits/sec receiver
iperf Done.
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-30.00 sec 2.03 GBytes 561 Mbits/sec sender
[ 4] 0.00-30.00 sec 2.03 GBytes 561 Mbits/sec receiver
iperf Done.
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-20.00 sec 323 MBytes 136 Mbits/sec sender
[ 4] 0.00-20.00 sec 323 MBytes 135 Mbits/sec receiver
iperf Done.
root@EA8500:~# ubus call system board
{
"kernel": "5.15.127",
"hostname": "EA8500",
"system": "ARMv7 Processor rev 0 (v7l)",
"model": "Linksys EA8500 WiFi Router",
"board_name": "linksys,ea8500",
"rootfs_type": "squashfs",
"release": {
"distribution": "OpenWrt",
"version": "23.05-SNAPSHOT",
"revision": "r23399-e74a4b509f",
"target": "ipq806x/generic",
"description": "OpenWrt 23.05-SNAPSHOT r23399-e74a4b509f"
}
}
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-30.00 sec 3.14 GBytes 898 Mbits/sec sender
[ 4] 0.00-30.00 sec 3.14 GBytes 898 Mbits/sec receiver
iperf Done.
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-20.00 sec 596 MBytes 250 Mbits/sec sender
[ 4] 0.00-20.00 sec 596 MBytes 250 Mbits/sec receiver
iperf Done.
Okay. So can this be resolved?
That is up to the devs, the patch may have unwanted side effects.
How would one apply the "patch" in the interim?
You have to compile yourself or perhaps if someone like @hnyman want to add the patch.
Edit:
The devs are working on a solution.
The patch we now have is actually reverting a Linux kernel patch and the devs are naturally hesitant to do that.
They are studying on a better approach.
If people are compiling themself and need instructions how to deal with this patch let me know.