Best firmware and settings for a dumb access point on netgear xr500(r7800)

Recently acquired a netgear XR500 and I am running it through its paces.

With 22.03.5 I am getting the following iperf3 performance over wifi using an iphone 13 pro as a client and an iperf3 server not running on the router.

Download: ~450 Mbps
Upload: ~650 Mbps

Are these in line with expectations for this router? That's an awfully big disparity between up and down.

During download I see the second core is almost pegged handling soft interrupts. I have eth0's irq assigned to that cpu core as that seemed to be the best performing of everything I tried, even though it pegs that core. The AP is trunked to my vlans via the AP's WAN port, thus the eth0 interrupts. Enabling packet steering didn't have any effect. I've also disabled the firewall so no bpf overhead at all.

Should I try anything else or is this as good as it gets? I don't think the NSS builds will help this use case (no natting going on) but could also be wrong about that. I also tried building the latest on 23.05 branch and wifi performance was roughly half. That actually seems like a regression.