Major fan of the RPi and finding new usable projects to engage in. My question is directly related to performance. What kind of performance should I expect out of building an Openwrt RPI? Currently I am running Pi-Hole + PiVPN + DOH on my network.
I'm a bit hoarder so I notice drops in bandwidth. If it's a security issue, I'll weigh the pros and cons of having something on my network that decreases throughput.
It amazes me as to what the RPi can handle, so I'm keen to know what kind of throughput I should be expecting.
Raspberry Pi has an architecture "oddity" in the way it connects its Ethernet NICs, limited by, as I understand it, USB 2.0 speeds. Being a "one-armed" device compounds the throughput issues in a routing scenario.
I haven't tested it myself, but the tests below suggest a 100-200 mbps throughput, limited by the NIC connectivity. You can get that or more out of a decent micro-router at US$20-40, and get 2.4 GHz wireless as well.
Some other, similar class machines have better connectivity for their NICs.
OpenWrt should 'perform' on it like just about any other linux distribution, that doesn't quite make an RPi a suitable routing platform though.
As jeff mentioned, its I/O performance is abysmal and stuttering, with only a single low-end wlan. You can find new dual-radio routers with significantly more I/O performance and good wlan starting around 40-55 EUR (with PSU, case, storage, delivered to your doorstep), with some interesting devices on the used market for 10-20 EUR.
The only thing a RPi might do better than entry level routers might be running VPN services, as those mostly need CPU performance, with rather limited I/O needs - but the higher end ARM based routers would kill an RPi in this discipline as well.