The max wired WAN to LAN speed I get is 50Mb (bits) using openwrt 18.06.1.
My old Buffalo router that's 6 years old and cost less than 1/3 the price gets 250Mb.
I have AT&T gigabit internet and get 930Mb when I just plug straight into their router.
What speeds should I really expect?
This 50Mb I get is straight after install. Fiddling with anything like offload doesn't make any difference. I've tried swapping cables and, obviously, wireless isn't any faster than wired.
While I don't have the r7800, but the very similar nbg6817, it is working fine -and with lots of performance to spare- with 100/40 MBit/s (PPPoE) for me; as-is and without flow-offloading enabled, ipq8065 should be fine for 350-400 MBit/s.