In 2016, when I had 1Gb/s fibre at my place, I used a 2011 and could get speeds of ± 850Mb/s to speedtest.net.
± 15 devices on the LAN/WLAN and approximately 15 FW rules + NAT, fasttrack enabled.
Was not on a PPPoE connection but DHCP with the ISP. Only other difference was the WLAN was not part of the LAN bridge config, used additional subnet on the wireless side. Only devices that used wired connections was my 2 sons (gamers), rest of LAN clients used wifi
Above can’t be compared with ± 50 active clients as I suspect with so many clients the number of smaller packets etc will impact performance, I never tested the throughput while doing a download from wifi and speedstest from wired though. When I did speedtests, all other client devices were idle while testing
EDIT: What I did find once, was that different browsers doing speedtest gave very different results, Google Chrome gave best results