Recent tests have demonstrated the performance capabilities of running WireGuard on a Raspberry Pi Zero. The device, which is capable of handling USB 2.0 speeds, showed significant speed drops when using WireGuard for bi-directional testing and internet speed tests. However, it still managed to achieve speeds of around 30-40 megabits per second for WireGuard traffic.

Source: https://oct8l.gitlab.io/posts/2019/140/wireguard-performance-with-a-pi-zero/