RPi 4B vs RPi 3B+ performance

Due to the RPi shortage I would love to replace the RPi 4B (with an USB/Ethernet adaptor) currently being used as my main router by a RPi 3B+ (with 2 USB/Ethernet adaptors) and keep the 1 Gbps* performance I am getting now.
Do you think it is possible, or despite all the adaptors are 1Gbps the different CPU performance will not allow that?


* In fact I am getting 520Mbps in the downloads and 120Mbps in the uploads due to my internet provider contract!

Stick to what you have, the RPi3 with its USB 2.0 system bus is inadequate for this.