Disclaimer: I'm not an expert and I cannot tell you if the results are better or worse. I just started playing around with DCam 3 a short while ago.
The interesting idea behind the DCAMx profiles are the "Chroma variants", which is a different way to change the saturation in the image, in a way that is difficult to achieve with the standard saturation control. I'm not sure how this affects colour fidelity, it is more about getting a pleasing result.
In regards to the gamut volume, DCAM 5 is extremely large, and to me is more a mathematical exercise to achieve a colour space that includes all visible colours. I would consider DCam 4 or Dcam 3 as more "general purpose" spaces, mainly for landscape / natural environments.
With regards to the gamma curve, it is not linear but a proprietary curve that J Holmes would not disclose the details. He claims it gives better results in the deep shadows among others (I have not performed any tests in this regards).
Regarding raw converters, LR does not allow you to select the DCam x profile with the standard "Open in PS" function, so you'd have to export to tiff and then open in PS. In contrast, ACR allows you to chose any profile, same with C1.
