I would like to have your viewpoint on the differences between the two PA’s QPM and OPP, especially when the scenario is that the organization has identified sub processes like Cost and Schedule Variance as selected sub processes and all the projects follow this organization wide. Now there seem to be lot of redundancy in that case among various practices of QPM as well as OPP.
Ahhh, the 'ol OPP vs QPM redundancy question!
I'll admit that back in the day I had similar issues with the high maturity process areas, but I've been to the SEI mountain, worshiped at the alter of high maturity, and been fully indoctrinated into the cult-like interpretation of the informative material! Just kidding, it's great stuff!
I understand that you've identified sub processes that your are monitoring and measuring, and that is great! But it's not quite what the practices are ALL about.
Think of OPP as setting up an infrastructure and engine for statistical monitoring and analysis - an infrastructure that the projects will later use while the execute processes based upon QPM. The projects also feed the engine, for OPP is a hungry one!
What kinds of things take place in OPP? Gaining a solid, statistical understanding of a selected set of sub processes and their performance. This understanding includes analysis such as the identification of the natural bounds of the process (within control limits) and the use of other methods to understand process performance. We call these "baselines." It also includes "modeling" which uses the data to predict what will happen (within limits) if certain actions are taken in the future. We call these "models."
QPM is the CONSUMER of the OPP baselines and models. When a project starts up, the PM will "compose" the process based on the project's goals/objectives AND the baselines and models made available to her via the OPP-related work.
So, for example, if the project is very high risk, with medium complexity, and a compressed time-frame, the PM might select sub processes from the set of standard processes that will help them succeed given those conditions. He also will constantly monitor the sub process performance using the tools and methods spawned by OPP-related processes to understand whether or not they are going to meet their objectives.
There is a clear delineation between OPP and QPM - one is a supplier, the other a consumer (and then ultimately a supplier BACK to OPP to feed the baseline data).