If 2 ESP's are used for the ESPnow server and ESP32 to MQTT connector and SPI is used for communication then use the ESP32 SPI API over the ESP32's Arduino Core. The number of SPI options go way up by using the ESP32's SPI API.
Also, ESP32's have a built in ODBCII module, the ESP32 still requires a ODBCII transceiver. I've got some really good transfer speeds in noisy environments and using long wires.