I also experienced the gigabit performance issue (Debian 9 and 10, APU4C4); estimate a bandwidth cap of about 400 Mbps, too. I don't actually have a need to exceed that speed on my home network, so I'm still happy. But also curious if anyone has built a beefier, more capable open source hardware router that also isn't a power hog.
There are also TLSense routers[0], which include configurations with Intels i5 [1] or i7. They also claim 7-15W power usage, AES-NI support, microphone/headphones jacks, HDMI, RS-232 and room enough for 16GB of RAM, which is quite unusual in routers.
