Is there a difference between the USB and RJ12 connections for the CSP V3 pedals?

There are no differences in resolution of the pedals when connection to either one of the two connectivity types. In terms of functionality, connecting the pedals via RJ12 to the wheel base allows for the Brake Force (BRF) function in the Tuning Menu to be available.  

Ensure that only one connection type is in use! Connecting the pedals via both RJ12 and USB at the same time can cause damage to the PCB of the pedal set