The RC4 is quite different in design to the DHX having a larger shaft to flow more oil in addition to this it has High and low speed compression adjustment which is a completely different design to the propedal/low speed compression system. It also has larger diameter piggy back chamber so a larger volume air chamber.
All shocks will benefit from a custom tune as they are built to a price (less so in the case of the CCDB) and are set for 'Joe average' weight and riding even when tuned for a specific frame. With a bit of porting on the piston (if applicable) and re shimming pretty much any shock with perform alot better, giving more sentivity and greater bump absorbtion.
With shocks like the Dueler, CCDB, Elka, and RC4 which have High and Low speed compression adjusters and in some cases pressure and volume adjusters on the gas chamber you can set them up to work pretty well but a gain to get the best out of them a bit of custom tuning will always help.