With x86_64 / AMD64 machines and external APs (formal APs, or all-in-one devices configures as APs) generally exceeding the capabilities of all-in-one devices.
You can take just about any old desktop PC, having 1 or 2 GB of RAM, put in extra Ethernet cards, use a USB flash drive as the system disk, and have a system that is way overkill for almost anything you'd want to do with OpenWrt.
The downside is will use a lot of electricity, so consider it as a temporary proof of concept. Buying a network appliance x86 type system with < 10 watts power consumption will rather quickly pay for itself.
The thing to look for when buying new (besides power consumption) is does the CPU have AES-NI support, this will greatly improve the performance of a VPN server or client.
That certainly does not qualify as "way above the average router" today with, for example, https://openwrt.org/toh/zyxel/nbg6817 running a 1700 MHz dual-core ARM SoC and 512 MB in an all-in-one package. Or, for that matter, the similar R7800 mentioned by the OP.