Originally Posted by TY@TEAMTEKIN

New solder posts that are shorter and have a different solder pocket design for easier connections.
New FETs which upped the amperage to 210 from the previous 180.
New BEC components.
Board composition also changed, striving for lower resistance.
Larger heat sink for increased cooling.

Just like when we revamped the RS PRO to the Black Edition, lots of changes were made that maybe aren't immediately apparent but they are there. Components evolve, we always want to use the absolute best quality we can, so the RSX went PRO since it is substantially upgraded from the previous version.