Believe it or not they can actually handle over 500Mbps up and down, did a speed test not so long ago with one on a 1Gb line, even a 10 year old Telkom router maxed it's 100Mb WAN port on the 1Gb line
I find that really hard to believe. Even the EdgeRouterX which has a fair amount of memory and processing grunt behind it, needs to be tweaked in order to get full synchronous 500/500.
With a lower range device like this, with firewall, traffic management, dhcp services and wifi traffic management all turned on, It doesn't make logical sense that it would perform well at higher speeds.