I'm looking for a simple, clean way of displaying a 'percentage complete

You can do that as well. I think we are talking about the looping logic. If you want it dynamic, then you need to interrogate the CDT at any given time and get the values. If I were to design your logic, I would have a separate variable holding the % complete as I dont see CDT the right place to store % complete as it doesnt really form part of the data model which CDT's are suppose to be. And in the logic where you do the looping, you would update the process variable. The advantage here is that the lifecycle of the process variable is now controlled by the lifecycle of the process instance and this in turn lines up nicely with the lifecycle of the instance dashboard and secondly and most importantly, updating the value and storing it back into the DB means that you now have to do two writes and two reads to the database which again can add overhead.

You can do that as well. I think we are talking about the looping logic. If you want it dynamic, then you need to interrogate the CDT at any given time and get the values. If I were to design your logic, I would have a separate variable holding the % complete as I dont see CDT the right place to store % complete as it doesnt really form part of the data model which CDT's are suppose to be. And in the logic where you do the looping, you would update the process variable. The advantage here is that the lifecycle of the process variable is now controlled by the lifecycle of the process instance and this in turn lines up nicely with the lifecycle of the instance dashboard and secondly and most importantly, updating the value and storing it back into the DB means that you now have to do two writes and two reads to the database which again can add overhead.