How to send a large amount of data faster ?

I'm trying to visualize your hardware setup.

1. Esp8266 with Espruino flashed into the Esp8266
   
2. Esp8266 connected via serial port to a Pico, Espruino board or Arudino.
   
   

The first case would be slower because the uP has to handle more tasks (marshall data to send, and send data)
The second cases have more than one uP to divide up the tasks.