i think about to by the WAC104 (https://openwrt.org/toh/netgear/wac104) to substitude my WNDR3700 to get better wireless- an routing performance. the wac104 seems to have a good cpu/ram and its form factor is small so it fits good in the livig room.
does soemething speaks against my thought to by a WAC104 / put openwrt on it? or are there better deals?
I could get a used R7800 for about 70 euro. perhaps i should prefer this device because in future i get a fibre connection with 500 Mbit ... r is this device too old, or is the atk-wifi chipset outdatet and better go with the xiaomi?
i also like the usb3 ports - so i could share harddisk in the network.
The r7800 is a great router, but it maxes out around 600-650 MBit/s using swconfig (currently around 360-370 MBit/s using multi cpu-port DSA), so I really wouldn't recommend it for a 500 MBit/s WAN connection anymore (not enough headroom for the future). Yes, the out-of-tree NSS acceleration support can extend this limit, but that's a bit risky to rely upon.
beside my wndr3700 (i use it as ap and router/vpn for my vdsl 50 mbit line) i have already one raspi 2 running here with raspian/debian-linux for my homeautomation (fhem etc). It works realy well and needs just 2 watts power consumption .
so it would be interesting to migrate the raspi 2 to raspi 4 (raspi 4 is suggested in your post) and add move the router-functionality to the raspi. but the raspi 4 is expensive and mostly out of stock / plus you need an extra usb lan card. and i need some more usb (2.0) ports for my home-automation dongles (onewire, knx-cul, ....). and if i want to boot the raspi from ssd rather from sd card to be more safe.
another idea that i have after reading your post is to use my old Lenovo X201 with docking-station. it has a build in ssd, 2 usb 3.0 ports via expresscard, much usb2.0 ports, ONE GBIT-Lan. but in idle mode it needs 13 watts ... so perhaps its not so good for 24/7 ... , and i also have to put the 2nd lan port via usb 3.0 ...
so perhaps its better to have two separate devices ... i leave my raspi 2 for homeautomation as it is ... and i search for a goot openwrt router/ap. (?)