How to improve Wireguard speed?

[Houman]

Hello,

I'm compiling the latest stable Wireguard on Debian 11.

git clone https://git.zx2c4.com/wireguard-tools
make -C wireguard-tools/src -j$(nproc)
sudo make -C wireguard-tools/src install

However the speed is not that impressive.  I have a VPS with 4 vCores
and 8 GB RAM on 1 Gbps network.  The VPS is located in London and so
am I.

With wireguard enabled I get 117 Mbps
Without wireguard I get 506 Mbps

That's a drop of 75%. What are the factors to improve the download rate?

Thank you,