I've used a single form successfully. I use a check off box and then allow the PA's to remain open provided the person responsible for tracking gets a monthly report of progress. It seems to work.
The real issue is defining what's corrective and what's preventive. That can be difficult whether you have one system or two.
I tend to use the CPAR form as a cover and collector form for any information relating to the project. In many cases, a section on the form may say "Refer to attached documentation".
I've also seen "preventive action" documented within a "continuous improvement" system. The system documents meeting minutes and any documentation (notes, letters, etc.) associated with the project.