If you are looking for a bit more power, you need to consider something with A53.
That said, I'm surprised you are having issues, considering I have done over 200Mbps using a MT7621A with its 800MHz MIPS CPU.
I think I was hitting 60+ Mbps though, so it wasn't all bad. However my home connection is 1000/100, so going above 100+ isn't going to mean much. Which is why I've been too cheap to invest in a Pi 4; not too great of an improvement for 55+ EUR investment.
I can't say for sure that it was because of the Wireguard tunnel, but considering how low my Wireguard usage was before without issues, it's my main suspect. After I got home, I hard rebooted the EdgeRouter and then migrated my DNS and Wireguard off of it. I've decided that the less things that my EdgeRouter X does, the better it is. I've also decided that if I get a new Raspberry Pi for my Wireguard duties, I'll leave the old one as a backup because you just never know.