Baja velocidad en red local vía wifi con Netgear XR500

Os escribo desde la desesperación y la ignorancia, buscando vuestra ayuda.

Dentro de mi red local tengo un pequeño NAS OpenMediaVault, funcionando sobre una placa Rock64. Conectada por cable gigabit directamente al router, un Netgear XR500.

Datos: Desde el iPhone, Speedtest: 565/540Mbps. Bien, tengo contratado 600/600. El wifi va bien.

Pruebas

Con iPerf de iPhone a iMac via wifi los dos:

Server listening on TCP port 5001
TCP window size: 128 KByte (default)
---
[ 4] local 192.168.1.6 port 5001 connected with 192.168.1.14 port 53368
[ ID] Interval Transfer Bandwidth
[ 4] 0.0- 0.1 sec 1.00 MBytes 142 Mbits/sec
[ 4] local 192.168.1.6 port 5001 connected with 192.168.1.14 port 53369
[ 4] 0.0- 0.1 sec 1.00 MBytes 137 Mbits/sec

Con iPerf de iPhone a iMac por cable:

[ 4] local 192.168.1.5 port 5001 connected with 192.168.1.14 port 53370
[ 4] 0.0- 0.3 sec 1.00 MBytes 30.0 Mbits/sec
[ 4] local 192.168.1.5 port 5001 connected with 192.168.1.14 port 53371
[ 4] 0.0- 0.2 sec 1.00 MBytes 54.9 Mbits/sec
[ 4] local 192.168.1.5 port 5001 connected with 192.168.1.14 port 53372
[ 4] 0.0- 0.2 sec 1.00 MBytes 38.2 Mbits/sec

Con iperf desde iMac a Rock64 por cable:

[ 4] local 192.168.1.10 port 5001 connected with 192.168.1.5 port 61533
[ 4] 0.0-10.0 sec 1.04 GBytes 893 Mbits/sec
[ 4] local 192.168.1.10 port 5001 connected with 192.168.1.5 port 57527
[ 4] 0.0-10.0 sec 1.07 GBytes 919 Mbits/sec

Con iPerf desde iMac wifi a Rock64

[ 4] local 192.168.1.10 port 5001 connected with 192.168.1.6 port 56934
[ 4] 0.0-10.7 sec 1.63 MBytes 1.27 Mbits/sec
[ 4] local 192.168.1.10 port 5001 connected with 192.168.1.6 port 52480
[ 4] 0.0-15.7 sec 640 KBytes 333 Kbits/sec
[ 4] local 192.168.1.10 port 5001 connected with 192.168.1.6 port 54822
[ 4] 0.0-28.6 sec 1.38 MBytes 403 Kbits/sec

Y por último, iPerf desde iPhone a Rock64:

[ 4] local 192.168.1.10 port 5001 connected with 192.168.1.14 port 53379
[ 4] 0.0- 7.4 sec 1.00 MBytes 1.14 Mbits/sec
[ 4] local 192.168.1.10 port 5001 connected with 192.168.1.14 port 53380
[ 4] 0.0- 0.2 sec 1.00 MBytes 33.7 Mbits/sec
[ 4] local 192.168.1.10 port 5001 connected with 192.168.1.14 port 53381
[ 4] 0.0- 0.2 sec 1.00 MBytes 42.9 Mbits/sec
[ 4] local 192.168.1.10 port 5001 connected with 192.168.1.14 port 53382
[ 4] 0.0- 0.3 sec 1.00 MBytes 28.6 Mbits/sec

¿Alguien me ilumina sobre por donde puedo tirar para solucionar este problema?